307 FXUS63 KMPX 121051 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 551 AM CDT Mon Jun 12 2017 .SHORT TERM...(Today and tonight) Issued at 428 AM CDT Mon Jun 12 2017 Main concern continues to be thunderstorm chances and timing. We have had a relative lull in the precip early this morning, as weak high pressure has moved into the Dakotas and Minnesota and upper heights have been rising. Front has moved just barely southeast of our forecast area, and stretches from central Wisconsin to northwest Iowa. Weak pattern means light winds overnight, and with all the precip yesterday, there is enough leftover moisture to result in widespread low clouds and dense fog this morning. The fog is quite shallow, and should disappear by mid morning. Have continued the dense fog advisory, and even expanded it to most of our area, except for south central MN to west central WI. High clouds and some modest amount of wind has kept the fog at bay in those areas. With a weak front, upper ridging and no apparent forcing mechanism early this morning, have lowered pops for this morning in south central MN. However, return flow sets up this afternoon as high moves off and weak short wave arrives. Thunderstorms will become possible again this afternoon, spreading from south to north as warm advection increases. There is some chance for severe weather in southern MN, but am not overly excited about it. Still, low level flow increases enough, and thermo parameters are conducive for storms, so will not be surprised if there are a couple storms this afternoon and evening that are severe. A better chance for storms will occur late tonight, when a much stronger short wave rotates around the broad upper low out west and sweeps across MN. .LONG TERM...(Tuesday through Sunday) Issued at 428 AM CDT Mon Jun 12 2017 Additional chances for severe storms are found early in the long term forecast period associated with the finale of the system that plagued the area with thunderstorms for several days. Tuesday & Wednesday are the days we will need to worry about as far as severe weather potential is concerned, when the warm front lifts from southern to central MN/WI (Tuesday), and the cold front awaits its turn to pass over the eastern Dakotas (Wednesday). The western half of the forecast area (roughly St Cloud to Fairmont) looks to have the highest threat for severe storms Tuesday afternoon, given the mid-level cooling (acting to erode the convective inhibition and steepen lapse rates) and enhanced deep layer shear that will result as the deep closed low ejects eastward from the Rockies to the Northern Plains and takes on a negative tilt. These pieces of the puzzle are expected to come together around 00z Wednesday over western MN. Storm mode looks to be supercellular in nature given the progged instability & shear parameters. Therefore, all severe phenomena (damaging winds, large hail, tornadoes) appear possible. The activity then spreads east across the forecast area on Tuesday evening, although there could be a weakening trend as storms pull away from the best forcing/cooling aloft. High temperatures on Tuesday and Wednesday look to warm into the mid 80s to lower 90s. Heat index values do near heat advisory criteria in the Twin Cities metro (95 degrees), but progged Wet Bulb Globe Temperature (WBGT) values only in the lower 80s illustrate the assistance breezy winds and cloud cover will have on lowering the heat risk somewhat. Wednesday brings the passage of the aforementioned cold front. We do lose a bit of the forcing given the low will have lifted to northwest Ontario. Therefore shear and flow look fairly weak, so the potential for organized activity is lower. Eastern areas (east of I-35) appear to have a slightly higher severe potential given closer proximity to height falls with the closed low to the northwest. However, plenty of residual instability will still be around as exhibited by progged dewpoints in the mid/upper 60s and precipitable water values around 2 inches. In the wake of the system on Thursday and Friday temperatures retreat back into the 80s for highs, which is cooler but still above normal for mid June. Weak westerly mid level flow and faint impulses could generate a shower or two, but overall dry weather is expected into Friday. Late Friday and Saturday the front lifts back norther toward the area, so we could see the return of a few showers and thunderstorms. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) Issued at 551 AM CDT Mon Jun 12 2017 Two main concerns...fog and thunderstorms. A shallow deck of low ifr ceilings developed overnight, mainly over east central MN and into much of the metro except for the southwest. Some of this is also in far western WI. The remainder of the area has shallow ground fog. Satellite imagery suggests the lifr will persist into mid morning. As for the storms, it looks like the next wave will arrive this afternoon, first in southwest MN, then spreading northward. The best chance in most areas seems to be this evening, though far western MN could see a lot more storms late tonight. KMSP...low ifr ceilings moved over the airfield just in the last hour, and they will likely remain for a couple hours before dissipating. Otherwise, the next weak short wave will arrive midday today, and it's conceivable KMSP will have storms by early afternoon. But it is more likely they will move in later later this afternoon. /OUTLOOK FOR KMSP/ Tue...VFR/MVFR with TSRA likely late. Wind S at 10-15kt. Wed...VFR/MVFR with TSRA possible. Wind S-SW 5-10kt. Thu...VFR. Wind W 5 to 10kt. KMSP... /OUTLOOK FOR KMSP/ && .MPX WATCHES/WARNINGS/ADVISORIES... WI...Dense Fog Advisory until 9 AM CDT this morning for WIZ014-015- 023. MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ041>045- 047>068-073>075. && $$ SHORT TERM...TDK LONG TERM...LS AVIATION...TDK