NWS Forecast Discussion

000
FXUS63 KDTX 201035
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
635 AM EDT Mon May 20 2019


.AVIATION...

A cold front will progress south of the area today, with WSW flow
becoming NW from north to south. MVFR to lower VFR cigs will remain
in place much of the day, but expect rapid clearing this evening as
high pressure begins to build into the area. This high will also
allow winds to decouple to 6kts or less by evening after gusting in
the neighborhood of 25 knots during the day.

.DTW THRESHOLD PROBABILITIES...

* High in ceilings aob below 5000 feet through this afternoon,
  medium this evening.

&&

.PREV DISCUSSION...
Issued at 346 AM EDT Mon May 20 2019

DISCUSSION...

Passage of the cold front early this morning will leave southeast
Michigan in deep layer westerly flow. Cold air advection behind the
front and departing low pressure system will result in a return to
cooler weather today. The colder air over southeast Michigan by the
afternoon will be characterized by 850 mb temperatures around 0C and
925 mb temperatures around 4C. The will allow for below normal high
temperatures in the 50s with plenty of boundary layer clouds hanging
around for much of the day. Breezy westerly winds will also be in
store for today. The mixed layer will be fairly shallow, but will be
able to tap into strong low level flow of around 30-35 knots
translating to surface gusts of 25-30 mph. Gradual clearing of clouds
from west to east late this evening into tonight brings an
opportunity for good radiational cooling and low temperatures to dip
into the mid 30s to low 40s. With forecast dewpoints hanging around
the mid 30s, patchy frost may have potential to develop if overnight
lows dip a little more than expected. Limiting factors will be light
gradient wind through much of the night and some high clouds creeping
into Lower Michigan. The most likely locations would be towards the
Saginaw Valley. Will hold off on any frost headlines, but it will be
something to monitor with the next forecast package.

There will be only minor modifications to the airmass by early
Tuesday with a broad surface high moving over the region. There will
be a subtle rebound in 850/925 mb temperatures with confluent flow
aloft bringing fewer clouds, which will aide in high temperatures
being able to rebound into the 60s. Upper level ridge axis will move
over southeast Michigan late Tuesday keeping conditions dry for the
remainder of the Tuesday period while a low pressure system
strengthens across the central plains.

The central plains surface low pressure system will be tracking
northerly in response to the pivoting of the upper jet across the
southern US Rockies while a secondary upper low dives southeast out
of the Pac NW and into southwest US. This will help draw a warm
front northward into Lower Michigan on Wednesday afternoon bringing
the next opportunity for precipitation. Anticipate only isolated
thunderstorms during the afternoon with limited instability over
much of the area when precipitation moves through. With the further
progression north of the warm front, better instability begins to
reach into southeast Michigan. This will allow for a better shot at
thunderstorms towards the evening and into Thursday morning with
sufficient shear to support some organized convection within a
corridor of theta-e and lower low level jet support.

Strong warm air advection behind the front will allow for
temperatures to reach above normal into the 80s for much of
southeast Michigan to finish the work week. On and off precipitation
chances Friday through the weekend as Michigan sits between a high
pressure across the southeast US and a low pressure drifting across
southern Canada. This will allow continued moisture to be drawn into
Michigan along with various shortwaves under persistent southwest
flow.

MARINE...

A cold front will shift south from Lake Huron to Lake Erie today.
Southwest to west winds will gust to 25 knots or more over Saginaw
Bay before decreasing this afternoon as the flow veers to the
northwest. Westerly flow will also increase over Lake St Clair and
western Lake Erie where wind gusts of 25 to perhaps 30 knots can be
expected today. Small Craft Advisories will be in effect for these
locations. The remaining nearshore zones will gust more in the 20 to
25 knot range due to the lack of fetch and a decrease in pressure
gradient along the front during the middle of the day.

Over the open waters, gusts of 20 to 25 knots will be common with a
period of 25 to 30 knots gusts within northwest flow over northern
portions of the lake late this afternoon/early this evening as a
secondary trough pivots just northeast of the area and briefly
increases the pressure gradient. High pressure will then build into
the area overnight tonight into Tuesday and bring light winds and
favorable marine conditions. 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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441.

Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this
     afternoon for LEZ444.

&&

$$

AVIATION.....DG
DISCUSSION...AA
MARINE.......DG


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NWS DTX Office Area Forecast Discussion