NWS Forecast Discussion

000
FXUS63 KDTX 091059
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
659 AM EDT Thu Apr 9 2020

.AVIATION...

Southeast Michigan airspace will reside within a cold west-northwest
flow through this taf period. The ensuing increase in diurnal mixing
will translate into a steady rise in gust magnitude through the day.
Peak gusts from mid afternoon into the evening reaching near or just
above 30 knots at times. The combination of daytime heating and cold
mid level conditions will support a scattered to numerous coverage
of afternoon/evening showers within an expanding lower VFR stratocu
field. Instability may prove great enough to allow for an isolated
thunderstorm, but the likelihood of occurrence remains very low. Any
higher intensity showers could lead to some small hail and/or a very
brief transition to snow, in addition to disruptions in visibility.
The loss of daytime heating will bring a corresponding decrease in
wind gust magnitude and coverage of low cloud/showers after 00z.

For DTW...A gusty northwest to westerly wind today, peaking mid
afternoon and evening from a 290 direction. Gusts near 30 knots
during this time, leading to crosswind considerations. Brief window
for clear skies across lowest 5000 ft late morning, then increasing
lower cloud this afternoon. Potential for afternoon/evening showers,
with an isolated thunderstorm possible. Thunder potential too low to
highlight attm. The more intense showers may result in small hail.

DTW THRESHOLD PROBABILITIES...

* Low in ceilings below 5000 feet through late morning. Moderate
  this afternoon and evening.

* Low in crosswind thresholds being exceeded this morning. High
  this afternoon and evening.

* Low in thunderstorm occurrence this afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 352 AM EDT Thu Apr 9 2020

DISCUSSION...

A strong cold front is dropping southward through SE MI at press
time. Obs show a strong thermal gradient with temps around 50
degrees ahead of the front and upper 30s immediately behind it. An
area of post frontal showers will spread across a portion of the
area over in the predawn hours. Meanwhile in the mid levels, a
trough with a potent lobe of vorticity will pivot through the
southern Great Lakes. The airmass behind this trough will be notably
colder with a 500mb cold pool passing around -35C passing over the
area this afternoon. 850mb temps will drop into the negative single
digits as well. The strength of the low and surge of cold air will
result in a handful of issues to deal with today.

A tight pressure gradient in the wake of the system with
strengthening northwesterly flow will result in gusty winds through
the day, and will actually carry through tonight as well. During
the afternoon, the surge of cold air will promote deep mixing with
the help of some early day heating. Models have been pretty
consistent the last few nights with a deep layer of winds in the 30
knot range throughout this mixed layer. So expectations are for
winds to become westerly and gust into the 30-40 mph range through
the daylight hours. Not much support can be found for advisory
criteria in the models or local probability graphs based on synoptic
conditions.

This takes us into the second main issue to deal with today,
afternoon showers. As we often see on these strong post frontal cold
advection days, steep low level lapse rates and degree of cold air
aloft will help produce some weak instability with around a hundred
J/kg of CAPE today (RAP on the higher side around 200 J/kg). This
should generate a generous coverage of showers through the afternoon
and evening until daytime heating ceases and boundary layer becomes
less favorable. Though rain showers should be the dominated Ptype,
these cold temperatures will make sleet/graupel possible within the
stronger cells. Could also see a few lightning strikes with the
strongest cells. The deeper mixing within the convection may also
produce some higher wind gusts to around 50 mph. We`ll deal with
these more isolated strongest gusts with an SPS or related product.

High pressure will build in on Friday which will loosen the gradient
and allow winds to relax. The thermal trough will still be overhead
which will keep temps down in the 40s yet again but should start
seeing some sun by later in the afternoon. Some moderation to the
airmass will take place heading through the weekend as the high
drifts across the TN Valley and low amplitude ridging aloft builds
into the Great Lakes. Temps should get well into the 50s once again
by Sunday.

Next system is on tap for the start of the new week as a cutoff low
over Southern California releases east. It will pick up some gulf
moisture before trying to phase with yet another strong northern
stream trough leading to more rain, cold temperatures and gusty
conditions.

MARINE...

A strong cold front has moved across the Central Great Lakes early
this morning. Cold air advection along with increased pressure
gradient from strengthening low pressure over the Eastern Great Lakes
will bring unsettled marine conditions today into tomorrow. Post
frontal winds will be out of the northwest with gale warnings in
effect across Lake Huron this afternoon into tomorrow morning.
Conditions will also result in Small Craft Advisories for all the
nearshore zones including western Lake Erie and Lake St. Clair. High
pressure builds into the region during Friday night leading to more
favorable marine conditions for the weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory from noon today to noon EDT Friday for
     MIZ049-054.

Lake Huron...Gale Warning from 6 PM this evening to noon EDT Friday for
     LHZ462>464.

     Small Craft Advisory from noon today to noon EDT Friday for LHZ421-
     422-441>443.

     Gale Warning from noon today to noon EDT Friday for LHZ361>363.

Lake St Clair...Small Craft Advisory from noon today to noon EDT Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon today to noon EDT Friday for LEZ444.

&&

$$

AVIATION.....MR
DISCUSSION...DRK
MARINE.......AA

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at www.weather.gov/detroit.

NWS DTX Office Area Forecast Discussion