Thursday, April 27, 2017

April to end wet, then a cool start to May

With the first in a series of storm systems behind us (last night's semi-bust [at least locally] of a perfectly good Enhanced/Moderate Risk scenario), we turn our attention to the last weekend in April, one in which there are many outdoor activities planned, including a Redbirds home-stand and at least a couple of civic festivals. Fortunately, the forecast has improved slightly from a few days ago, at least for part of the weekend.

Preliminary storm reports from April 26 overlaid on the morning SPC outlook. While there were about 200 wind and hail reports for the day, except for a string of reports that extended well beyond the Slight Risk area in the Midwest, reports were fairly scattered and there were zero tornado reports, the basis for the Moderate Risk. (NOAA/SPC)

Friday: Gulf opens up

After a pleasant spring day on Thursday with highs near 70 and comfortable humidity, Wednesday night's front returns north on Friday morning as a warm front. The passage of the front means the arrival of humidity levels we haven't seen yet this spring as dewpoints climb to near 70 degrees or a bit higher. You'll notice the sticky-ness when you leave work or pick up the kids in the afternoon, as well as the return of gusty south wind signaling that the Gulf is open for business.


A couple of showers are possible during the morning as the front surges north and low pressure starts traveling along the front to our west, then there's a chance of a few thunderstorms in the afternoon, though models differ on that prediction. If they do develop, there will be a good deal of instability so gusty wind and pockets of hail are possible in any strong storms. High temperatures reach the lower 80s, and if the sun peaks through the clouds some in the afternoon, perhaps mid 80s.

Convective Available Potential Energy (CAPE, or instability, aka "storm fuel") forecast by the GFS model on Friday evening will be very high - more than enough to fuel strong storms, IF they form.

Friday Night: borderline

The fireworks really start along the front on Friday evening as thunderstorms explode to our north. A corridor from OK across northern AR into the Ohio Valley will see multiple rounds of storms with heavy rain Friday night. The metro is right on the southern edge of where rain will fall and chances vary based on the model scenario you want to buy. Northern areas definitely have a better shot at rain than north MS, but we could all stay dry too. For now, we'll carry a generic "chance of thunderstorms" until it becomes a little clearer. The corridor to our north will not only be prone to some flooding, but also severe weather, including large hail and damaging wind.  An Enhanced Risk (category 3/5) is outlooked as far south as I-40. Our threat locally is conditional on storms actually occurring. Once again, if they happen, they could be strong. Temperatures won't drop below 70 degrees Friday night.

The severe weather risk is Enhanced (3/5) for areas north of I-40 on Friday night. If storms form this far south, they could be severe. Chances of them forming in the metro are about 30-40%. (NOAA/SPC)


Saturday: summertime

Saturday may be our first taste of early summer as the front remains well to our north and gusty southerly wind indicate the Gulf is still open, leading to continued high humidity. With some sunshine expected, temperatures that start near 70 will soar into the 80s and perhaps close to 90 in spots and the term "heat index" may be bantered about as it will likely eclipse 90 for the first time in 2017. With the heat and humidity in place, there appears to be a chance of some afternoon "peak heating" thunderstorms not atypical of a Mid-South summer day. If storms form, they could again be strong with high wind gusts the main threat. Outside of storm gusts, general wind will be very gusty throughout the day as well, peaking at 25-35 mph and perhaps higher.  If you have outdoor plans, keep them. If you have outdoor objects, secure them. If you're a vendor at a festival, leave the brochures at home.

The European model, which we rarely show, highlights the potential for strong wind gusts on Saturday, perhaps approaching 40 mph at their peak. (WxBell)



Sunday: wet

The weekend ends with a very wet, windy, and potentially stormy day. The system to our northwest finally gets pushed back to the southeast by low pressure that moves out of the southern plains. Rain starts early, maybe before dawn, and continues for several hours. The GFS and European models differ on when the front arrives to shut off the spigot, but it will likely be no earlier than mid-afternoon and possibly as late as the evening. Rain could be heavy with 2-3" possible during the day.

The Weather Prediction Center forecasts rainfall for the entire weekend in the 2-4" range in the metro, but over 6" not too far away in AR and MO. Expect this to lead to additional rises in local and main stream rivers like the Mississippi into next week.

In addition, there are indications that it could be one of the windiest days in a long time, especially if the front lingers to the west until late in the day. Gusts have the potential to reach 40-50 mph, perhaps stronger in storms that are also expected. Saturated soil and strong wind could be enough to down some trees. Stay tuned, as the models still need to come to some consensus.

Next week: below normal temps

Once the big system moves out Sunday night, spring returns early in the week with dry air, cooler mornings, and pleasant afternoons. One more system that brings a chance of rain mid-week will be followed by an even cooler spell, just in time for Beale Street Music Fest! Let's hope for a great weekend for the massive party on the river!

In the meantime, Go Grizzlies!!


Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Monday, April 24, 2017

Another stormy pattern takes shape as April winds down

A wet weekend marked by chilly temperatures is in the rear-view mirror with the early part of the work week defined by more typical springtime temperatures in the mid 70s to near 80 degrees and abundant sunshine. However, as you might expect, you should savor these days as they don't typically stick around for long! We're back into a wet - and stormy- pattern by Wednesday that carries us right to the end of the month.

As high pressure responsible for the mostly sunny sky and warm temperatures shifts east, southerly flow is re-established and a cold front makes its approach by the middle of the week. Ahead of the front, Gulf moisture will raise dewpoints into the 60s on gusty south wind, sufficient to support thunderstorms. In addition, there will be enough instability and wind shear to support the threat of a few severe storms. The daytime hours Wednesday should be mainly dry, but as the sun sets, look for a line of storms to be moving quickly across AR, pushed by a cold front.

According to the GFS model (which is supported by our other models), dewpoints in the 60s, sufficient for heavy rain and thunderstorms, will be in place Wednesday evening as a cold front moves across the region. (PivotalWeather)

The GFS model also predicts sufficient instability and low level shear (combined, we reference as the "Energy Helicity Index") to produce a threat of rotating storms, capable of damaging wind, some hail, and a tornado or two on Wednesday evening. Plan ahead if you have ball games or other outdoor activities Wednesday night. (PivotalWeather)

The line will move across the metro during the mid to late evening hours or most likely between 7pm-midnight Wednesday. The severe weather risk is higher just to our west, but as indicated by the graphics above, is also possible in the metro. [UPDATED Tuesday, 6:30am] An Enhanced Risk of severe storms (category 3/5) is forecast for areas just west of the metro with a Slight Risk (category 2/5) covering metro Memphis. This outlook will be updated again on Tuesday afternoon and a few times Wednesday and could change based on newer information from the computer models. For now, be prepared for the possibility of damaging wind and perhaps some hail or a tornado. Heavy rain (an inch or more is possible) and lightning are likely.



Thursday will see high pressure build briefly back into the region, but by Friday, low pressure over the Plains will set the stage for additional storms, some of which could be severe heading into the weekend. Our best chances for storms appear to be late Friday into early Saturday, then again Saturday night and Sunday. The daytime hours Friday and Saturday MAY catch a break based on the latest model data, but the weekend situation is very dynamic and could easily change. Once again, somewhat like last weekend, periods of heavy rain appear likely. Right now I'd say Sunday is the most likely day we could experience heavy rain during daytime hours. Rainfall totals from Wednesday evening through Sunday could be in the 3-6" range, more than we got last weekend by a factor of about 2.

The Weather Prediction Center believes we could be in line for 3-6" of rainfall over the next week from multiple systems that affect the region. (NOAA/WPC)

As for severe weather threats, there could be a chance of damaging wind and hail Friday night and all modes of severe weather (wind, hail or a tornado) on Sunday. The current outlooks from the Storm Prediction Center for Friday through Sunday is shown below. Again, these WILL change multiple times between now and then, but this is a heads up that you need to remain weather aware as we approach the weekend.

Severe weather probabilities for the weekend from the Storm Prediction Center show an active pattern in the south-central U.S. A 15% probability equates to a Slight Risk and means that there is a 15% chance of severe weather (hail, wind, or tornado) within 25 miles of a point inside the area. A 30% risk equates to an Enhanced Risk. (SPC) (Click here if the image does not loop.)

Stay up to date with the latest forecast from MWN via our website and mobile apps, and via our social media channels and blog, all linked below.

Side note: current conditions from Bartlett, TN are unavailable in our apps and website due to weather station maintenance. We expect this outage to last through about May 5 and certainly apologize for the inconvenience!

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Wednesday, April 19, 2017

April (heavy) showers in the forecast

The rainfall deficit in Memphis so far this year is about 6" with about half of that since March 1. A wet system this weekend looks to put a dent in that deficit with the potential for heavy rain and some thunderstorms affecting springtime outdoor activities. Let's dig into the details.



Wednesday and Thursday

A front earlier this week is basically a non-factor now as we head into the middle of the week and start making plans for the weekend. A few pop-up showers are possible this afternoon and again Thursday afternoon, but coverage should be minimal with temperatures well into the 80s (10°+ warmer than average for this time of year).

By Thursday night, a cold front drops south into the metro and brings a chance of showers and thunderstorms. I expect the evening hours to only have small chances, but they'll increase overnight as the front stalls along I-40 like rush hour traffic with multiple accidents in progress. If you're headed to FedExForum to cheer Fizz and the Grizz and chide the refs, you should be in pretty good shape, though some rain might start to fall in sync with the streamers from the rafters about 11pm (#TakeThatForData)!


Friday

The front will likely stall along the I-40 corridor all day (because that's why I-40 exists - for fronts to know where to stop). Building instability to its south over north MS and energy in the mid levels of the atmosphere going by to its north will result in scattered showers and thunderstorms during the day and into Friday evening. There could be a few strong storms during the PM hours, especially over north MS.

The North American Model (NAM) shows the front roughly along I-40 Friday afternoon with instability ("storm fuel," measured by CAPE) along and south of the front where the best chance of storms will exist. 
The entire area is currently outlooked under a Marginal Risk (category 1/5) of severe weather, which means a few severe storms are possible, but chances are low. Where the front stalls will be key as the best chance of strong storms, as well as potentially some heavy rain, will be along and south of it. Temperatures will remain in the 70s most of the day.

A Marginal Risk (category 1/5) of severe weather exists Friday across the area. A couple storms could contain strong wind. 
On Friday night, low pressure over OK will move east into AR and start to pull that front back to the north, putting the metro in the "warm sector" of the approaching low by Saturday morning. Expect more thunder as it does so, as well as some downpours and breezy southerly wind. Friday and Friday night activities need to have a rain plan if you're risk tolerance is low.

Saturday

The low pressure system in AR looks like it'll also take I-40 eastbound and move just about over Memphis by mid-day. Models differ some on placement of the low, the warm front pulling north, and timing of a cold front that the low drags across the area. However, without trying to nail down exact details, expect Saturday to be a wet day, and potentially a washout for at least a portion of the day. As the low draws near, thunderstorm chances increase markedly, as does the likelihood of heavy rain. Right now, the morning and early afternoon hours are most "under the gun," with conditions improving steadily as we head towards Game 4 Saturday night.

The NAM model expects low pressure to be nearing the metro, dragging a cold front (blue line) towards the MS River by early afternoon Saturday. The red line is a warm front that had previously stalled along I-40 on Friday.
The Storm Prediction Center has the equivalent of a Slight Risk (category 2/5) of severe weather forecast for Saturday and I can't argue that. Instability should be sufficient, wind energy is expected, and a potent low will move right over us. That could be the recipe for a few strong storms with wind and hail threats. The tornado threat doesn't look too high right now, but where there's a low and a warm front, we have to consider that a possibility.

The day 4 (Saturday) outlook places the metro in a 15% risk of severe storms, equivalent to a Slight Risk. Areas ahead of the low and south of the warm front will have a risk of strong wind, hail, and an isolated tornado. Our threat ends with the frontal passage Saturday afternoon.
I believe the threat of flash flooding is more widespread than any of those threats right now though. Most areas in the Mid-South will likely see 2-3" of rain between Thursday night and Saturday evening with a good deal of that Saturday. Some spots could see 3-4" or more if storms train along the front. My concern is actually for spots that see heavy rain prior to Saturday, as that could set the stage for Saturday's rain being all run-off due to wet ground. Fortunately, this month has been fairly dry so far.

Total rainfall forecast through Monday morning. Widespread 2-3" totals are likely over the next 4-5 days. (NOAA/WPC)

Sunday into next week

Withe the low to the east and northwest wind wrapping around it, Sunday will be cooler and likely start off cloudy with clouds diminishing by afternoon or evening. A stray shower is possible as temperatures that start near 50 get no higher than the mid 60s on gusty northwest wind. It'll feel more like early spring than the early summer we have started to notice lately!

Early next week promises a return to nice spring-like conditions with abundant sunshine and highs in the 70s, rising to 80 by Wednesday. Sounds like something to look forward to!


Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Thursday, April 13, 2017

Easter Weekend Forecast: warm with increasing rain chances

It certainly has warmed up over the past couple days! Spring is definitely as it starts to feel a little like early summer during the afternoon hours. Temperatures are more than 10 degrees above our normal (comfortable) highs for this time of the year - the lower 70s. With Easter weekend upon us and outdoor activities really starting to ramp up, let's unwrap the details on how long the warm weather may last, and whether there's any rain in the forecast!


Friday

With high pressure re-establishing over the east coast and an upper level ridge in place, plus very little recent rainfall (which converts some of the sun's energy to evaporation rather than heating), we should be looking at warm temperatures very similar to Thursday. After a morning low in the lower 60s, the high should once again be in the mid 80s. The record is 88°. A stray shower or two can't be ruled out, but the rain chance should be 20% or less. Though warm, I proclaim it a GOOD Friday!


Saturday

The pattern changes little over our area other than a slight weakening of the upper level ridge of high pressure, so a few more clouds are expected but rain chances will be fleeting. With southerly wind blowing a little stronger and a bit more cloud cover, we'll see slightly warmer morning lows (mid 60s) but similar highs in the afternoon (83-85°). A great day for Easter egg hunts or any outdoor plans you have!



Easter Sunday

With the high breaking down a bit more, a weak front will move to a position north of the metro, but additional cloud cover is expected as well as an increase in humidity south of the front. If you're up early for sunrise services, look for a mild morning with temperatures in the mid 60s. By afternoon egg hunts, we could see a few showers around the area that could throw a wrench in your plans, though most activity will be to our north (northeast AR and northwest TN) closer to the front. Highs should again reach 80°, if not a touch warmer depending on cloud cover and rain chances.



Next week

As we head back to work and school, the front works it's way south a little further and rain and thunderstorm chances increase. Monday could be a day we're dodging raindrops off and on most of the day. Tuesday looks similar, though with high pressure starting to build back in, rain chances could be limited to the afternoon hours when it's warmest.

By mid-week, the high over the southeastern U.S. looks to be re-established and the storm track (which could be "stormy") should round that high well to our west and north. We'll watch for that to break down by late in the week. Temperatures early next week will generally be in the upper 70s to lower 80s for highs and 60s for lows - still above normal for this time of year.


Erik Proseus
MWN Meteorologist

----
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