NWS Forecast Discussion
FXUS63 KDTX 202258
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
658 PM EDT Mon May 20 2019
An increasingly dry and stable environment as high pressure builds
into the region will bring a steady clearing trend from northwest to
southeast late this evening. This environment will maintain mostly
clear skies across the lowest 5000 ft through Tuesday, outside of
perhaps a few diurnal cu. Prevailing northwest winds diminishing in
speed overnight, then shifting to east-northeast on Tuesday. High
clouds thickening from south to north throughout Tuesday.
.DTW THRESHOLD PROBABILITIES...
* High in ceilings aob below 5000 feet through the late evening.
Issued at 325 PM EDT Mon May 20 2019
It has been a chilly late May day across Se Mi as temps have largely
remained in the low-mid 50s with westerly winds gusting in the 20 to
30 MPH range. Surface high pressure will expand into Lower Mi from
the west during the course of the night, tucked under a region of
mid level confluence. The resulting low level anticyclonic flow and
loss in diurnal mixing will support a clearing trend during the
evening, possibly into the early overnight. Veering of the low level
flow toward the northwest and the southeastward expansion of the
Lake Mi marine layer will cause the clearing to take hold from
northwest to southeast tonight. As the sfc high builds in overnight,
winds will become light, supporting decent radiational cooling. This
cooling will be limited to a degree by an increase in mid/high level
clouds late tonight, mainly south of the I-69 corridor. The Saginaw
Valley and thumb region, where evening clearing will be the earliest
to occur will see the greatest degree of cooling, with mins likely
dipping down into the 30s. Lows in the 40s should suffice elsewhere.
Given that the low levels remain relatively moist (sfc dewpoints
still around 40) only patchy frost will be mentioned across the
Se Mi will lie between a deep upper level low rotating across the
central high plains and an upper low moving into the Canadian
maritimes on Tuesday. This will result in a sharpening mid level
ridge axis across the Great Lakes, sustaining the sfc high across
the region. There will however be a forced transport of higher mid
level moisture into srn Mi during the day Tuesday within the
entrance region of an impressive 160 upper jet max over ern Canada.
Model solutions suggest this moisture combined with some mid level
frontal forcing will support some showers across nrn IN, possibly
far SW Lower Mi on Tuesday. As mid level heights build during the
day, this frontal circulation is shown to weaken. This and a fairly
substantial sub 700mb dry layer will support a dry forecast Tuesday,
although there will be ample mid and high clouds through the day.
Some moderation in the low level thermal profile will allow Tues
high temps to make a run at lower 60s, with cooler readings near the
lakes under onshore flow.
With the plains upper low forecast to lift into the northern plains
on Wednesday, strong low-mid level southwest inflow across the Ohio
Valley will drive mid level moisture and an elevated instability
plume into Se Mi. Timing looks to be late Tues night into early
Wednesday. Fairly steep mid level lapse rates within this moisture
feed will be supportive of a good chance of showers and
thunderstorms. There will be a strengthening of the low level
southeast flow overnight Tuesday into the day Wednesday with the
approach of the sfc warm front. This may lead to yet another round
of water level rises and flooding concerns along the shores of Lakes
St Clair and Erie. There is a fair amount of model agreement in
suggesting the warm front will lift into Se MI late Wed. The
timing/placement of this front will have substantial impact on
temperatures Wednesday as it will replace a cool marine modified
airmass with a more summer-like temperature/humidity regime.
Thursday, southeastern Michigan will have shower and thunderstorm
chances from a weak cold front trailing a shortwave located north of
Lake Superior. This is quickly followed by a small ridge of high
pressure that will be over the state on early Friday. By late Friday
evening shower and storm chances return and linger through the day
Saturday as a warm front moves across SE MI. This front is tied to a
low that will be moving northeast from the plains into Minnesota. As
the low moves into Ontario and Quebec, the trailing cold front is
looking to stall out near or just south of the Ohio border. This
becomes a stationary front that will keep rain chances for counties
along the Ohio border from Saturday night through Sunday.
West-northwest winds this afternoon gusting to around 25 knots this
afternoon will slowly decrease this evening and shift to the
northeast overnight as high pressure builds into the area through
tomorrow, providing light winds and favorable marine conditions
during the day. East to southeast flow will then increase on
Wednesday as this high shifts to the east and a warm front lifts
north towards the area. However, winds are expected to stay under 25
knots along the nearshore waters, and small craft advisories may not
be needed. Winds become southwest late Wednesday night ahead of a
cold front, which passes through on Thursday. Gusts up to 25 knots
are possible right along the shoreline areas of the nearshore
waters, with low level stability over the open waters holding gusts
generally under 20 knots.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.
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NWS DTX Office Area Forecast Discussion