Thursday, April 28, 2016

Memphis in May starts this weekend - so of course it's going to rain!

Last year, the first weekend in May, and by association the Beale Street Music Festival, was blessed with amazing weather. But as you might expect from "Memphis in Mud," consecutive years would be taking it a bit too far! So, get those galoshes, rain boots, and ponchos ready (because umbrellas aren't allowed), and let's dig into the details of what to expect this weekend, whether you're headed downtown, to Arlington in April, or just having a spring garage sale!


Though the general pattern from Friday through Sunday is a wet one, there will definitely be some "lulls" as it won't rain the entire weekend. Hopefully this will provide some idea of when those might occur. A couple of "up-front" notes: severe weather chances are very low, so we don't expect any large hail, high wind, or tornadoes to strike a crowded outdoor event. However, rain will be heavy at times and lightning is also expected. We recommend you have a plan for what to do if you start hearing thunder - and standing under a lone tall tree ain't it.


Friday

The pleasant spring weather we've had today quickly gets inundated by Friday's lunch hour as low pressure forms over west TX, pulling a warm front north from the Deep South into the Mid-South. While the morning hours will be mainly dry, the afternoon will be mainly wet with periods of heavy rain possible, but minimal lightning.

The surface map for mid-day Friday shows a stationary front to our south as it gets ready to move north. Dark green is where highest rain chances are and the area to our west will expand east during the afternoon hours.
As the warm front approaches in the evening, some thunderstorms will also be likely and rain could continue deep into the overnight hours. Rainfall amounts Friday afternoon through early Saturday will likely be pretty close to an inch with much heavier amounts to our west. Again, severe weather is not expected. Temperatures Friday will top out in the upper 70s and remain mild (near 70) in the evening hours.

The "most likely" precipitation total map through midnight Friday night indicates 3/4" or more of rain is expected with the initial wave of precipitation Friday.  2-3" may fall across  parts of Arkansas.

Saturday

The daytime hours Saturday will probably see a break from the steady rain with just scattered showers or thunderstorms possible. Honestly, I wouldn't be surprised to see some fairly lengthy dry periods from morning through mid-afternoon. With the warm front to our north and the next cold front well to the west, there won't be a lot to trigger storm initiation outside of a weak passing upper level disturbance. With gusty southerly wind pushing temperatures to near 80 and very humid air in place, it won't take much to pop off a few thunderstorm cells though, so I'm not willing to call it a dry day.

By Saturday night, the low pressure center will be moving across the Missouri River Valley, dragging the cold front closer and rain and thunderstorm chances increase. If it stays fairly dry during the day, perhaps even with a peek of sunshine, instability will be pretty high, so lightning and thunder appears likely by evening. Severe weather chances should remain minimal with the main threats being a strong gust of wind or small hail, besides heavy rainfall. Evening temperatures will again be in the 70 degree range. Total rainfall Saturday and Saturday night could be another inch or so.

The surface map for Saturday early evening shows precipitation chances increasing again as a cold front approaches from the west. By Sunday morning, that front will be along the Mississippi River, marking an end to steady precipitation. Thunderstorms will also be possible as the front approaches Saturday night.

The "most likely" precipitation totals map for the period Saturday morning through the overnight hours Saturday night shows another 3/4" or so of rain will fall. 

Sunday

The cold front moves through Sunday morning. It's passage should end just about all rain chances, though a post-frontal trough could wrap around the low to our north and bring a shower or two. Overall, we believe chances are low and by noon we should start seeing some sunshine. The rest of the day looks downright pleasant with highs in the upper 70s to near 80 and a breeze with a northerly component whisking the humidity to the south.

Total precipitation forecast by the NWS through Sunday afternoon indicates at least 2" of rain is expected in the Memphis metro this weekend.
Overall, we advise keeping rain gear handy and remaining weather aware throughout the weekend. We'll be nowcasting for the entire metro throughout the weekend on our social media channels below with an emphasis on Music Fest. You'll also be able to find radar, live tweets, and more through our mobile apps for Android and iOS (links below). Stay safe and stay dry (if possible!).

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Tuesday, April 26, 2016

Tuesday PM update - storm chances through Wednesday

UPDATED - 6:50pm CDT:
This evening's threat is waning as storms are having trouble departing MO and are weakening as they do, thanks to a cap of stable air they are attempting to sink south into. Our overnight chance of rain is now just 20%. The rest of the blog regarding tomorrow is still on track, including weakening of morning storms before they get here.


ORIGINAL POST - 3:10pm:
A warm and muggy day today has resulted in cloud cover over the area most of today, a sign that humidity is increasing as we head into a stormy pattern. The regional radar loop (shown below - always current) as of mid-afternoon shows a complex of storms extending from the St. Louis area west across MO.

Current regional radar loop. As of mid-afternoon storms are just coming into the picture in central MO as they drop southeast towards the Mid-South.
This complex will continue move southeast and is our first "fly in the ointment." As it moves south, it will encounter very moist air that is also unstable and will remain that way well after dark. Most models think it will either fall apart or move by to our northeast after dark. However, one of the more reliable short-term high-res models says "not so fast." If it's right, we could see some lightning and thunder between 10pm-2am. Severe weather is not expected locally, but a few strong storms are possible as the line moves into northwest TN early in the evening.

Once that passes, we turn our eyes to the west, where an outbreak of severe storms will be ongoing in the eastern and southern Plains. A line of storms is expected to cross AR by the wee hours Wednesday and will likely affect the metro after rush hour Wednesday morning. Once again, I expect we'll see a weakening line that will be in a state somewhere between scattered showers and a broken line of non-severe storms, depending on which model you believe. Either way, no morning severe weather is expected at this point.

HRRR (high-res model) "simulated radar" though 3am shows the MO storm complex grazing the metro and the Wednesday morning system approaching from the west. Graphic courtesy WxBell. 
However, the morning system will have a direct impact on what happens the rest of the day. The best bet is that we'll see a few peeks of sun by mid-day and the atmosphere will "re-energize" as the day goes on and as a cold front approaches from the west. The entire Mid-South is in a Slight Risk (category 2 of 5) for the potential for strong to severe storms to develop and move through the metro.


The primary risks will be large hail and damaging wind, though a tornado is possible. I also expect we'll see some refinement to the severe weather outlook tomorrow once the effects of morning rain on the overall state of the atmosphere are better understood. An Enhanced Risk (category 3/5) outlook is entirely possible somewhere in the Mid-South. The most likely timing for PM strong storms will be from mid-afternoon through about midnight, with additional refinement also expected as we head into tomorrow. If you have evening activities outdoors, we strongly recommend a plan B and to stay weather aware. (Yes, I know it has rained for about 1,512 Wednesdays in a row...)

After Wednesday, Thursday looks warm and dry with storms possibly returning by Friday evening and lasting off and on throughout the weekend.

Below are some tips to review prior to our severe weather threat - know them and share them! In addition, we highly recommend you have multiple ways of receiving severe weather warnings, no matter if you are at work, home, or asleep. Pros and cons of multiple ways are shown below as well.  One of those ways, if you have a smartphone, is to have StormWatch+ severe weather notifications set up via the MemphisWeather.net mobile app. Links to more information and downloads are at the bottom of this post. Stay tuned to our social media accounts also listed below for the latest information!



Stay safe!

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+ .
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Sunday, April 24, 2016

Time for the A/C, but how about our storm chances this week?

A beautiful spring weekend is about in the books; hope you got a chance to get out and enjoy it! A little warmth crept into the area as high pressure shifted to our east, allowing warm southerly air to move in. With almost no cloud cover, highs reached 80°+ each day this weekend, but humidity levels were still comfortable and morning lows were very pleasant (in the 50s).

The surface map for Sunday night shows high pressure on the east coast bringing warm, southerly flow into the Mid-South, while a storm system organizes in the Plains.

Monday and Tuesday

As we head into the last week of April and towards the first weekend of Memphis in May, the warming trend will continue with a few chances of thunderstorms from the middle of the week into next weekend. Starting early in the week, dry weather continues as the focus for strong to severe thunderstorm activity focuses on the central and southern Plains. With increasing humidity, expect cloud cover to also be more prevalent than the weekend, though partly cloudy will suffice for Monday and partly sunny for Tuesday. Look for highs to reach the lower to mid 80s with lows in the 60s and warm southerly wind throughout. A shower or thunderstorm is possible Tuesday, but most areas will remain dry.

By Tuesday evening, a few showers or thunderstorms will be possible in the area, while severe storms are expected in the Plains. The cold front to our west will move into the region Wednesday bringing high chances of thunderstorms and perhaps a chance of severe weather.

Wednesday

The central U.S. storm system will make a push east on Wednesday which is our next best chance for thunderstorms. The Storm Prediction Center has a 15% chance of severe weather (equivalent to a Slight Risk, or category 2/5) for areas west of the Mississippi River on Wednesday. However, that could easily change as both the American GFS and European models indicate storms could roll into the Memphis metro late Wednesday afternoon and evening, which is when instability is maximized due to being during peak heating hours. The PM hours Wednesday will be worth monitoring, with storms possibly continuing into the overnight hours. It's too early to define exact storm threats and timing, so stay tuned.

The Storm Prediction Center's severe weather outlook for Wednesday indicates possible severe weather from MO/IL south across the western Mid-South into northeast TX.  This scenario will bear watching as the outlook are will be adjusted daily as the system draws near. Severe weather threats are TBD at this time.

Thursday and Friday

Though the medium-range models disagreed a bit the past few days, they are now converging on a solution that would keep Thursday and perhaps most of Friday dry as weak high pressure builds in behind Wednesday's system. Expect some sun, but likely not "sunny" days with continued warm temperatures, probably in the 80s for highs and 60s for lows.

Next weekend

As we head towards next weekend and Beale Street Music Fest, the crystal ball gets a little fuzzy. Long-range solutions from the computer models offer various solutions, but it appears that scattered thunderstorms will be possible again late in the week as a warm front pull back north across the region. Then, things get even more murky as to when the next cold front moves through, ranging from Saturday PM (European model) to Sunday PM (GFS/Canadian models). For now, we'll call next weekend "unsettled" with daily chances of thunderstorms. The one thing we are fairly certain of is that it won't be as cool as last year's Music Fest. Hopefully it just won't turn in to another Memphis in Mud!


As many of you know, MWN is the Official Weather Partner of Memphis in May, so we'll be keeping a close eye on the weekend and will also keep you abreast of changing conditions, including updates from Tom Lee Park during Music Fest. Stay up to date with our latest thoughts on storm chances via the human-powered MWN Forecast on our mobile apps or on the web.

Speaking of which, the Android app has a new update out (with iPhone releasing in the upcoming week) which adds a couple of features, including the ability to read these blog posts within the app and adding Drummonds, TN to our current conditions providers. We also updated some "under the hood" stuff that will keep StormWatch+ on top of its game. With severe weather season upon us, we strongly recommend you consider having a smartphone option for severe weather alerting and our StormWatch+ service is one of the best! Download links can be found below.

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+ Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone. Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Friday, April 15, 2016

Weather 102: The Omega Block and its effects on our upcoming weather

It's been a dreary and cool couple of days as an upper level low pressure system has moved SLOWLY over the region. As we head into the weekend, we have one thing to say to Mr. Upper Low:


As of Friday morning, an upper level low pressure system was over the region with it's counter-clockwise flow and unsettled weather, resulting in clouds and showers that moved little.
Yep, we're kicking the upper low to the curb and setting up a fairly interesting and "weather nerdy" pattern as we head into the weekend and early next week. Today, I introduce you to the "Omega Block." No, it's not something the anesthesiologist gives to numb a section of the body. An Omega Block is a weather pattern in the upper levels that, when plotted on a map, resembles the Greek letter omega, or an upside down horseshoe. The "block" term comes from the fact that the pattern tends to persist for a while and blocks the forward progression of air masses. Here's the mid level (18,000 foot) map for mid-day Saturday:

By mid-day Saturday, the Omega Block will set up over the eastern U.S., with its distinct inverted horseshoe shape at the mid levels, which will keep weather systems at bay to the west.
The black line with arrows represents the flow of air at 18,000'. Notice it's shape - like an omega symbol. The atmospheric setup is basically strong low pressure over the Four Corner (which is resulting in a major snow storm for the Denver area and Rockies east of the Continental Divide), low pressure over the west-central Atlantic, and a large area of high pressure covering the eastern half of the country between the lows. Air flows counterclockwise around the lows and clockwise around the high, resulting in the huge ridge between the lows.

Because the ridge forces the jet stream up and around it, air doesn't flow from west to east like normal, but has large bends north and south. Warm and dry air is found under the high, while cool and stormy weather is found on either side of the block. This is fairly obvious in the surface map valid Saturday at 1pm that shows a lot of precipitation, particularly on the west side of the high, with a large dome of dryness under the ridge.

The surface map and 12-hour accumulated precipitation for mid-day Saturday shows the effects of the Omega Block quite well. Stormy weather around the periphery of the block and dry and warmer weather under it.
For the Mid-South, we'll still have lingering clouds tomorrow, despite the ridge taking over at the upper levels, as flow in the low levels will be from the southeast, pulling moisture around the south side of the surface high pressure area. However, we will start to warm up a bit and by Sunday we'll see a lot more sun and temperatures that reach the mid to upper 70s.

As we head into next week, the Omega Block breaks down after a 3-4 day run and the low over the Four Corners fills, or weakens, as it moves northeast into the Plains. This will shift the stormy weather east, bringing rain and thunderstorm chances into the Mid-South from the west. The upper level pattern becomes more "zonal," or west-to-east, which will allow the low to progressively move closer and bring clouds and rain chances. However, temperatures will still likely be in the mid 70s most of next week as lows remain mild, or near 60.

By mid-week, the block will break down and the upper level low on the west side of it will move into the Plains. Flow across the southern U.S. will be "zonal," allowing weather systems to move a little more freely. However, the overall flow will be rather weak as the primary jet stream is well north in Canada, resulting in the Plains low being fairly slow moving.
The surface map for the same time as above shows the surface low and frontal systems across the mid-section of the country, which will increase our rain chances again heading into the middle of the week. 

So the next several days break down something like this...


And looking even further ahead, the Climate Prediction Center indicates that much of the CONUS, and especially the eastern half, will have high probabilities of above normal temperatures for the last week in April. Who's ready for some 80s??

NOAA Climate Prediction Center outlook for the last week of March indicates a 70% chance of above normal temperatures. Perhaps our first string of highs in the 80s as we approach May?

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador || Erik Proseus is an NWA Digital Seal Holder