Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 241655
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1255 PM EDT WED AUG 24 2016
700-500mb forcing has given rise to a narrow band of showers that
will approach the TAF sites at or shortly before valid time.
Additional development behind this line and an increase in weak
echoes warrants carrying TEMPO -SHRA through the early and mid
aftn hours. Encroaching cloud deck presents a forecast issue as
cigs will no doubt lower, but MVFR is slowly eroding with diurnal
heating. Prefer to reserve MVFR mention until arrival of deepest
moisture w/ rain this evening. MCV over NE Illinois will bring a
high probability of rain with embedded TS to the Detroit area this
evening. Environment in the wake of this wave will be favorable
for fog or some low stratus.
//DTW Threshold Probabilities...
* High for cig aob 5kft
* Medium for tstorms impacting KDTW airspace
Issued at 1128 AM EDT Wed AUG 24 2016
Decent MCV over Northern IL will track across far Southern Lower
MI this afternoon. The hi-res models all have a robust response to
this feature and thus will up the POPs into the likely category
for 16z-20z for the Tri Cities region and after 20z for the rest
of the forecast area.
Severe threat appears to be rather minimal. Ahead of the MCV, ML
CAPEs will struggle to get above 500 J/kg. A 30kt low level jet
feeding on the back side of the MCV may advect enough instability
that the trailing storms may be able to use some ML CAPEs around
1000 J/kg. That may be just enough instability with 0-6km bulk
shear approaching 25-30 kts to get one or two isolated severe
storms. The low level jet will also be advecting some good
moisture as precipitable waters get to around 2 inches. While the
storms should continue to move to the northeast around 30 mph, the
high water content with the forcing on the back side of the MCV
continuing to feed the system could lead to several rounds of
storms with heavy rainfall for a few isolated locations. That
would lead to an isolated flooding threat especially if that were
to occur over an urban area.
Subsidence behind this MCV will end most of the shower and storm
threat after about 02z until the next convective system moves into
the state from the west and southwest around 12z Thursday.
Issued at 327 AM EDT Wed AUG 24 2016
Most noteworthy part of the forecast will center around potential
for showers and thunderstorms today and Thursday, as well as a
return to humid conditions. Shortwave trough pushing across Iowa and
Wisconsin will lift across Michigan today, embedded within broad
southwest flow between a large upper trough advancing through
central Canada and and upper level high over the Deep South.
Increasing southwest flow will advect in warmer air and moisture
over the next few days. There will be a small risk for a shower or
even a thunderstorm during the mid to late morning on the leading
edge of strong theta-e advection and weak isentropic ascent.
Thinking, however, is that the dry air currently in place (evidenced
by 24.00Z DTX raob) may only allow for virga at best. The better
chance for showers/tstorms will arrive in the afternoon as the upper
shortwave crosses the area, and as dewpoints in the mid-60s to near
70 advect in from upstream. Mixed layer CAPE values around 1000 J/kg
(per GFS) and some dry air in the lower levels may allow for an
isolated severe wind gust to 60 mph during the afternoon and
evening, but widespread severe weather is not anticipated. Humidity
will also increase today as dewpoints rise, combining with slightly
above normal temps to create heat index values in the low to mid
80s. Overnight lows will also remain quite warm (close to 70) as
dewpoints remain elevated.
Additional moisture looks to arrive tonight and Thursday as the
approaching upper trough taps into a plume of monsoonal moisture
seen on water vapor imagery extending north of New Mexico and West
Texas. Latest model runs raise PW values up near 2 inches once
again. Still expecting fairly quiet conditions overnight as weak
shortwave ridging and subsidence build in behind the shortwave.
Models continue to show some smaller shortwave features tracking
near the MI/OH border however, and will retain lower chance pops
there. Upper trough will track into Ontario Thursday, pushing the
surface trough across Michigan during the afternoon. Showers and
thunderstorms should again develop by afternoon ahead of the trough
in a warm and humid airmass. A few stronger storms could develop
near the Ohio border where a mid-level speed max will strengthen
wind fields. Storms will also be capable of very heavy rainfall
given tall skinny CAPE profiles on forecast soundings and high PW.
Warm start to the day and continued warm air advection will favor
max temps solidly in the 80s, with heat indices south of M-59
reaching above 90 assuming no interference from early day
Drier air will work into the area behind the surface trough and then
especially behind a cold front that will arrive overnight. High
pressure should provide dry weather for both Friday and Saturday.
Temperatures will cool into the mid 70s to low 80s, with lower
dewpoints providing much more comfortable conditions. Upper trough
working across the Great Lakes will then bring the next chance for
showers and thunderstorms Saturday night through Sunday night,
however coverage at this time looks low as better forcing slides
north of the area.
A warm front will move through the lakes Wednesday afternoon/evening
bringing scattered showers and thunderstorms. A cold front will
follow shortly behind the warm front across northern Lake Huron and
slowly drop southeastward during the day Thursday and clear to the
east and south by early Thursday night. More scattered showers and
thunderstorms are likely with the cold front. Winds will be modest
from a southerly direction ahead of the warm front then tone down a
bit after passage. Winds will become northwesterly Friday behind
cold frontal passage. High pressure will bring light and variable
winds Saturday then more southerly Sunday as it moves off to the
east and a cold front approaches from the west. This front may
bring showers activity across Lake Huron Sunday afternoon.
A trough of low pressure will track through the Great Lakes region
today and Thursday. Shower and thunderstorm potential will increase
along a a warm front that will lift through the area today, then
persist along a cold front as it pushes southward across the state
on Thursday. Basin rainfall averages of around .50 inch will be
possible north of M 46 through Thursday, while basin rainfall
averages to the south of M 46 may range between .50 and 1.00 inch.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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