Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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012 FXUS63 KMPX 041901 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 201 PM CDT Thu Jul 4 2024 .KEY MESSAGES... - Thunderstorms and locally heavy rainfall likely today and tonight. - Numerous chances for showers and a few thunderstorms will linger into next week with temperatures remaining below normal. && .DISCUSSION... Issued at 159 PM CDT Thu Jul 4 2024 Our first round of rain today is currently located along the I-94 corridor and slowly moving northeast. Rainfall amounts from this activity has resulted in generally 0.1-0.2" with up to 0.5" within the very isolated heavier cells. Behind this first round is a brief clearing, evidenced by the lack of returns on radar and thinning clouds and small clearings on satellite over southern MN. However, in our weakly stable environment, it won`t take much for new convection to develop with a little daytime heating as the mid-level jet and vorticity maximum moves in from the west. Indeed, scattered showers and thunderstorms are in the process of developing across southwestern MN late this morning. This activity will move northeast, growing in coverage into scattered broken lines of cells, reaching the Twin Cities around 2-3 PM and western WI later this afternoon. The best chance of severe weather remains in southern to southeastern MN along I-90 where enough heating should result in 1500-2000 J/kg of MLCAPE within 35-40 knots of bulk shear. A weak tornado or two is possible within the surface vorticity rich environment near the surface low, but the main threat from any stronger storms will be large hail. Heavy rain will be possible with any thunderstorms, as PWATs range from 1.2-1.4" and vertical profiles are very moist. Though, the transient non-continuous nature of the storms should limit the flash flooding risk to a large degree. Nevertheless, rounds of storms with rainfall rates of 1-1.5" per hour over the same area could lead to localized flash flooding. This will be especially true as we progress through tonight, as the precip becomes more favored from south-central MN into northwestern WI. Precip in southeastern MN should decay with the dissipating instability while precip within the deformation zone north of the occluding surface low will be favored as synoptic lift increases. Showers and thunderstorms will wrap westward around the surface low as it travels east, meaning that a county wide or two area could see heavier rainfall rates for a period of 2-4 hours. This could lead to localized areas of 3-4" of rain while elsewhere from south-central MN to western WI will see rainfall of 1-2.5" by 12Z Friday. The low pressure system will slowly move east-northeast out of our area by early Friday afternoon with lingering, but decaying wraparound precip exiting with it. However, isolated showers and a thunderstorm may occur across MN during Friday afternoon underneath the backside of the upper-level shortwave. While the aforementioned shortwave will move east into the Great Lakes Saturday, a broader longwave trough will settle in over the Northern Plains/Upper Midwest through at least early next week. This will result in stagnant, mild temperatures (highs in the mid 70s to lower 80s into Monday). Additional chances for precipitation will also be possible Saturday through at least Tuesday as embedded impulses round through the trough. The heavy rain and severe weather threats don`t appear to be significant with any of the impulses, but don`t expect a prolonged break in the wet weather just yet. However, long-range forecast models do suggest the trough finally exits to our east during mid-next week. At the same time, a strong upper-level ridge will move into the western CONUS, with pieces of this ridge potentially spilling over into the central CONUS the latter half of next week. This signals a potential warmer, drier summer pattern occurring eventually for our region (also supported by the 6-10 and 8-14 Climate Prediction Center Outlooks) sometime within the next 2 weeks. We just need to get through a few more days of rain first. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1234 PM CDT Thu Jul 4 2024 Main aviation concern will be the ongoing showers and storms, which will last through this evening for most. A cluster of storms are currently developing over south-central MN, which would bring MVFR/IFR visibilities during the heaviest rainfall rates. A bit of a lull in precipitation is still expected late this evening/night, before rain showers and MVFR/IFR ceilings become more widespread overnight into tomorrow morning. Winds will remain generally light and variable today, before shifting out of the N/NW and increasing slightly tomorrow. The strongest thunderstorms, which could have wind gusts up to 50 mph and hail greater than an inch, are expected to stay further south near and along I-90. KMSP...The first wave of showers have passed this morning, and the focus turns to the redevelopment of precip to the southwest. Most of the cells over south-central MN are still elevated, so the threat for severe weather is lower, but reduced vis and thunder will still be likely. Storms could move in as early as 1:30-2pm, and would be off and on through the early evening. Cigs are still on track to drop to low MVFR by this evening and will likely become IFR late tonight through tomorrow morning. Isolated showers/storms are possible tomorrow afternoon/evening, but confidence is low so have kept mention out of the TAF for now. /OUTLOOK FOR KMSP/ SAT...Chance PM MVFR SHRA/TSRA. Wind SW 5-10 kts. SUN...MVFR/SHRA/TSRA likely. Wind SW 10-20 kts. MON...VFR, chance MVFR. Wind WNW 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...CTG AVIATION...BED