Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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981 FXUS63 KMPX 201746 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1246 PM CDT Mon May 20 2024 .KEY MESSAGES... - Slight potential for strong to severe storms across southern Minnesota this afternoon. - Increasing likelihood of strong to severe thunderstorms Tuesday PM across southern Minnesota and western Wisconsin. SPC day 2 SWO brings an Enhanced Risk (3 out of 5) into SE MN. - Heavy rainfall is likely and totals may exceed 3 inches through mid-week. This will likely lead to rises on rivers and their tributaries into the holiday weekend. && .DISCUSSION... Issued at 322 AM CDT Mon May 20 2024 Currently a mid-level low spins over the Dakotas and is forecast to prog east over MN/WI today. Convection has already begun initiating ahead of a warm front that extends from west-central MN over to Eau Claire, WI. Severe weather is not expected with this initial band of storms however, some of the stronger storms could produce pea size hail and brief gusty winds. Broader forcing associated with a cold front currently resides over Western MN where mainly showers and embedded thunder exists. This band of precip will spread over central and southern MN early this morning and begin to clear from west to east just after sunrise. There will be a few hours and some partial clearing to the skies later this morning into the early afternoon with highs into the mid-70s. The aforementioned boundary that brought the early morning precip, will become stationary as a trough over the inter-mountain west begins to become negatively tilted. This will force a potential MCS to develop over SE Nebraska, and SW Iowa. Its expected that system will lose its support and become disorganized. With that said however, another afternoon of convection does look possible. Forecast soundings showing an environment that features 0-6km shear nearing 30kts and elevated 1500 J/kg of MUCAPE thus allowing for the potential for gusty winds and large hail which aligns with the SPC`s slight risk (level 2 of 5) across southern MN. Although given the questionable forcing mechanisms, kept only slight mention of PoPs in the grids for now. Rainfall amounts through today will range between a tenth to a half inch, with locally higher amounts associated with stronger cells. By Tuesday into Wednesday, the trough over the intermountain west will eject a Colorado low towards the northern plains and intensifies by the time it reaches MN/WI. Like with previous discussions, the MSLP for this low pressure is forecast to reach climatological minimums per the ensemble situational awareness table and the return interval for a system of this caliber for late May comes about once per decade. A defined gradient in temperatures will exist from Duluth, MN down to Sioux Falls, SD. Areas north and west of this gradient will struggle to reach 60 degrees whereas mid 60s to low 70s to the south and east. As this low pressure progs through, widespread rain and thunderstorms will occur. The kinematics for convection do look favorable for more severe storms Tuesday afternoon which is highlighted in the SPC Day 2 Outlook for southeastern MN under an enhanced risk (level 3 of 5). A slight risk for severe storms is forecasted north and west including the Twin Cities as there are uncertainties with northward progress of the system`s warm sector. Primary hazards will be a few tornadoes based on forecasted hodographs, gusty winds, and large hail. NBM QPF totals still holding high confidence that much MN and western WI could see at least 1 to potentially 3 inches of rainfall through Wednesday night. Wednesday also looks to be the coolest day of the week with highs in the mid 60s and lows in the 40s. Thursday features a lull in the precipitation as a brief ridge of high pressure progresses overhead. Temperatures will return to the 70s and lows in the 50s. Some more rainfall tries to sneak back in on Friday and again on late Sunday as another series of shortwaves develop and make their way east across the Northern CONUS. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1224 PM CDT Mon May 20 2024 A busy stretch of weather is expected through this forecast period. MVFR/IFR cigs have been slow to move out through early this afternoon, despite guidance saying otherwise. Decided to keep things on the pessimistic side because of this. MVFR/IFR conditions are expected through the majority of the period once showers and thunderstorms move through late this evening into Tuesday afternoon and beyond. Timing still remains the tricky part of the forecast with hi-res guidance all over the place for a round of showers and storms before 06z for our southern sites. Most agree that all will see rain with embedded storms from 12z through the end of the period. Wind gusts may be underdone by Tuesday morning, but will wait until later forecasts to adjust. KMSP...The TAF is long and ugly to say the least. Based on ob trends, kept MVFR cigs through mid afternoon. While we have plenty of instability building this afternoon, we are lacking any sort of lift to initiate thunderstorms until the LLJ kicks in later tonight. Thinking there will be a break between the first and second round of storms overnight with chances once again increasing just before sunrise. A lot of uncertainty surrounds the midday Tuesday timeframe, but yet another round of storms is expected during the afternoon. These storms may be strong to severe with heavy rain and possible LIFR conditions into the evening. However, confidence is too low to include that in the TAF at this point. /OUTLOOK FOR KMSP/ WED...MVFR bcmg VFR. Chc -SHRA. Wind W 15G25kts. THU...VFR. Wind W 10 kts. FRI...VFR/MVFR chc -SHRA. Wind SE 10-15kts. && .HYDROLOGY... Issued at 655 AM CDT Sun May 19 2024 A heavy rain event remains on track for Tuesday, with a large footprint of 1 to 3 inches of rain, with some locations pushing 4 inches. The greatest rainfall totals are expected across southwest, west central, and central MN. Exactly where and how much rainfall we see will determine where a threat for river flooding will exist going into Memorial Day weekend, but given current rainfall forecasts, flooding during the holiday weekend may be possible in the Cottonwood, Redwood, Minnesota (upstream of Mankato), and Crow river basins. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...Dunleavy AVIATION...Dye HYDROLOGY...MPG