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Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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507 FXUS63 KMPX 050402 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1102 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. && .UPDATE... Issued at 818 PM CDT Thu Jul 4 2024 We`re all but done with phase one of this system with the primary WAA band of showers and storms now exiting stage right. Phase two is associated with the upper low that on water vapor imagery was centered between Willmar and Olivia at 8pm. Lift associated with the upper low is helping force the showers we see near the upper low and that trend will continue through the night as the upper low slowly moves east. For the metro, despite the less than ideal weather during the day, any firework shows still planned to go on this evening should find a window of dry weather to get those off before showers return for the rest of the night with the upper low. Severe risk the rest of the night is gone with the loss of instability. The excessive rain risk looks minimal as well as rain rates have come down considerably. Still the showers associated with the upper low are moving slow and locations that get under these downpours could pick up a fairly quick half inch of rain before they move on. && .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 /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1047 PM CDT Thu Jul 4 2024 We`ve moved off to phase 2 of this system and thats rain associated with the upper low itself, which at 11pm, water vapor imagery showed being not far from Litchfield (KLJF). Rotating around this low as been a broad shield of light to moderate rain with some embedded downpours. As the low slowly track ESE through the night, these areas of showers are expected to follow the upper low. Besides the rain, the expanding IFR/MVFR obs we`re seeing with obs is supported by moist low levels in RAP soundings and we expect extensive MVFR/IFR stratus through the night near the surface low that is slowly taking shape between MSP & MKT. CIGS will slowly improve through the morning, with another round of diurnally driven scattered shra/tsra expected Saturday afternoon. Have included PROB30s to cover that threat. HREF is most bullish with activity Saturday happening west of I-35, so kept MSP/EAU/RNH dry after the upper and surface lows clear the area in the morning. KMSP...We expect one more round of shra to move through MSP overnight as the upper low passes nearby. 8z-12z looking to be the window when -shra is most likely. For Saturday afternoon, MSP looks to have enough influence in the subsidence region of the departing upper low to suppress diurnal activity. /OUTLOOK FOR KMSP/ SAT...Chance PM MVFR/SHRA/TSRA. Wind SW 5-10 kts. SUN...VFR. Chc aftn SHRA/TSRA. Wind SW 10-20 kts. MON...VFR. Chc aftn SHRA/TSRA. Wind WNW 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ UPDATE...MPG DISCUSSION...CTG AVIATION...MPG