Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000 FXUS63 KMPX 050927 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 427 AM CDT Thu Aug 5 2021 .SHORT TERM...
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(Today through Friday) Issued at 426 AM CDT Thu Aug 5 2021 A disjointed upper level trough extends across the Dakotas into the southern High Plains and will spread across the upper MS valley this morning. A long front extends from southern James Bay, across northern Ontario, to the sfc low in SE Manitoba. The cold front trails off into ND and will be the driver of short term forecast period as it moves across our CWA this afternoon. Current radar imagery shows a broken line of showers that is moving across central and southern Minnesota. Recent trends indicate weakening as the line approaches the Twin Cities metro so I`ve decreased PoPs through mid-morning. A trace or few hundredths is possible with another round of showers and thunderstorms this afternoon as the surface boundary moves through. Highs will range from the mid 70s across western WI to upper 80s across western MN. Cloud cover will begin to break up and allow for heating across the western half of the CWA. Pre-frontal instability will build throughout the day with MLCAPE values approaching 1500-2000 J/kg by 21z. Strong post-trough boundary layer heating will aid buoyancy and increase the scattered thunderstorm development this afternoon and evening. Weak vertical shear and modest lapse rates should limit severe potential but the Storm Prediction Center has placed us in a Marginal Risk, primarily for gusty winds associated with the stronger updrafts and storms. QPF amounts will be highly dependent on if storms move over a particular location otherwise little to no rain is expected. For those lucky enough to see a storm a quick half inch to three quarters of an inch is possible. Things dry out overnight into Friday as the front moves into the western Great Lakes. Rising heights build in aloft and will lead to rebounding temperatures across the entire area. It`ll be somewhat pleasant for early August with highs ranging in the lower to mid 80s and dew points in the 60s. .LONG TERM...(Friday night through Wednesday) Issued at 426 AM CDT Thu Aug 5 2021 The pattern will be more active, with an upper low moving across the area this weekend, but after that, there are quite a few differences in the long range models, both deterministic and ensemble members. Therefore there will be modest chances for rain much of next week, mostly in the 20 to 30 percent probability range. There is relatively good agreement in the upper level pattern Friday night through Sunday. An upper low now approaching northern California should reach the northern high plains Friday night, with a weak short wave out ahead of it. A low level jet will set up just to our west as the upper low moves closer. Moisture transport looks excellent as precipitable water values of at least 1.5 inches will arrive with southerly flow from the western Gulf. The first batch of rain should arrive Friday night into Saturday midday, with mostly light amounts in our area. The main question will be Saturday afternoon into Sunday when the upper low arrives. The ECMWF does not seem to suggest much of a severe weather threat, but other models do, with questions about placement. The timing of the departure of the first wave will affect the amount of clearing and recovery of temps. The GFS does show mid level lapse rates around 7C/km, plus 0-6 km shear of at least 30 knots, with a couple pockets of stronger shear. Throw in a surface low in eastern SD as well. However, much will depend on how the upper low tracks. Most models suggest it will intensify Saturday night, but also drop south somewhat, moving across Nebraska and Iowa. At the very least, it does appear that rain should move across the area Saturday night and Sunday. After that, the pattern becomes even more uncertain. There are enough ensemble members suggesting broad upper west-southwest flow and an active pattern to merit precipitation chances throughout the coming week, but only on the order of 20-30 percent. A few ensemble members from both the GEFS and EPS suggest dry weather, but overall, it does look more active with occasional chances of rain.
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&& .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1057 PM CDT Wed Aug 4 2021 VFR conditions. A few light showers are possible overnight, but visibility should remain above 6 miles. There could be some thunderstorms at KMSP and KMKT late Thursday afternoon/evening, so did continue with a Prob30 group. KMSP... VFR conditions with a few light showers possible toward morning. Then we should have a break, with a chance for thunderstorms around 00Z. These will be scattered, so continued with a Prob30. Then expect winds to become southeast. /OUTLOOK FOR KMSP/ Fri...VFR. Wind S 5 kts becoming N 5-10 kts. Sat...VFR. SHRA/TSRA/MVFR likely late. Wind SSE 10-20 kts. Sun...VFR. Chc SHRA/TSRA/MVFR. Wind SSW 10-15 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ SHORT TERM...BPH LONG TERM...TDK AVIATION...JRB

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