Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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502 FXUS63 KDTX 161709 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 109 PM EDT Sun Jun 16 2024 .KEY MESSAGES... - An excessive heat watch remains in effect Monday afternoon through Friday evening. Several days of highs in the 90s are expected this week, with afternoon heat indices of 95 to 100. - Nighttime lows will only drop into the 70s over most of the area this week. - Scattered showers and thunderstorms tonight/Monday and Tuesday afternoon will bring potential of localized torrential rainfall. && .AVIATION... VFR conditions hold today into tonight within ridging with initial cluster of showers/thunderstorms over Lake Michigan bypassing the region to the north/northwest this evening (relatively close call for KMBS though). Will introduce prob30/tempo groups for early Mon morning thunderstorm as 12z model suite has latched on to solution which will bring small MCS/cluster of convection into the area. The mesoscale system bringing this activity is currently tracking thru SE IA/NE MO with active convection early this afternoon. A veering LLJ of 30+ knots will usher in much higher theta-e air overnight into Monday and this should allow for this system to fester all the way east into the area before dissipating by mid morning as LLJ forcing wanes during diurnal convection min. For DTW/D21 Convection...A small cluster of thunderstorms will be possible early Monday morning (first guess 10z-13z). With a rapid increase in moisture during this period, localized downpours could be quite heavy within certain pockets of this cluster. DTW THRESHOLD PROBABILITIES... * Low for thundestorms impacting the terminal ~10z-13z. * Low for ceilings aob 5kft with convection Monday morning. && .PREV DISCUSSION... Issued at 325 AM EDT Sun Jun 16 2024 DISCUSSION... A mid level short wave impulse over Iowa will track across Upper Michigan and eastern Lake Superior this afternoon and evening. CAMs solutions indicate the southern portion of the associated region of convection will generally weaken/fall apart as it approaches central Lower Mi this afternoon as a result of the dry and stable airmass entrenched across Se Mi. Veering of the low level flow toward the south-southeast today will advect much warmer air into Se Mi (925mb temps pushing +22C). While large scale subsidence may limit mixing depths to a degree, model soundings and probabilistic guidance supports afternoon highs in the mid to possibly upper 80s, with cooler readings near the lakes. The forecast for the remainder of the week will revolve around the development of an abnormally strong mid level ridge (heat dome) across the Mid Atlantic and Ohio Valley and the resulting heat wave that is expected to affect southeast Michigan. The expansion and strengthening of this ridge will begin tonight and persist into midweek. Increasing southerly flow circulating around this ridge will drive very warm air into Se Mi by Monday. The lead edge of higher mid level moisture will expand across Se Mi tonight. Despite steep mid level lapse rates arriving in tandem with this moisture plume, model soundings indicate the moisture capped by a warm layer. This will limit convective chances to isolated. Growth of the daytime mixed layer on Monday will drive afternoon highs into the mid to possibly upper 90s under continued low level warm air advection. Model soundings suggest the low level moisture will be shallow, which will allow some drying of the boundary layer through diurnal mixing. This should keep heat indices relatively close to actual air temperatures. There has been some degree of model agreement in suggesting some short wave impulses lifting into Se Mi within a plume of deeper moisture Tuesday/Tuesday night. This will warrant a chance of thunderstorms. The GFS ensemble members have been a little more bullish with moisture, resulting in greater convective coverage and thus a little cooler daytime highs (upper 80s to mid 90s). With a little higher sfc dewpoints, afternoon heat indices will likely rise well into the 90s, pending timing/coverage of any convection. By midweek, medium range model solutions show 500mb heights to be an anomalously high 598-600 dm centered over the Mid Atlantic. This ridge is forecast to undergo some westward expansion across the Ohio Valley from mid week into next weekend. Subtle placement differences in the ridge axis and southward extend of the baroclinic zone forecast across the northern Great Lakes will have some impact on high temperatures across southern Michigan. The GFS and its ensemble members have been a little farther south with the ridge axis with greater convective chances over southern Michigan, thus a little cooler. The ECMWF and Canadian solutions have been farther north and warmer across Se Mi. In fact, several ECMWF solutions have extreme heat persisting into next weekend. Based on the latest array of ensemble members and trends in the 00Z model suite, there is enough confidence in a prolonged period of heat to issue an excessive heat watch for all of Southeast Michigan through Friday. This watch will be issued for the cumulative effects of multiple days of high temperatures in the 90s and warm nighttime conditions as opposed to a specific day or two when heat indices may break 100. MARINE... A warm and humid airmass will set up over the Great Lakes today through early tomorrow morning and will last through the end of the week. This will produce relatively stable near surface lake conditions. Showers and thunderstorms remain possible today, focused mainly across northern Lake Huron initially through this morning, with a second round possible this afternoon and evening for all of Lake Huron and the Saginaw Bay. Some strong thunderstorm induced wind gusts aoa 30 knots and/or hail cannot be ruled out with today`s late day activity. This stronger storm potential will be favored across northern Lake Huron. Additional isolated to scattered shower and storm chances will exist tomorrow and Tuesday over the Great Lakes as an upper-level disturbance moves over the region. Otherwise, south to southwest flow will become established through early next week after the passage of the warm front. Some breezy conditions with gusts to 20-25 knots will be likely today as flow transitions from southeast to south-southwest, but otherwise gusts stay around or below 20 knots through the early week with the stable conditions in place. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Excessive Heat Watch from Monday afternoon through Friday evening for MIZ047>049-053>055-060>063-068>070-075-076-082-083. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DG DISCUSSION...SC MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.