Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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781
FXUS63 KDTX 161643
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1143 AM EST Fri Feb 16 2018


.AVIATION...

Lift associated with a short wave trough that will track across Se
Mi early this afternoon combined with diurnal mixing will continue
to result in some lifting of the strato cu base, possibly to MVFR.
Can not rule out a few flurries with this wave, particularly around
MBS and FNT. A push of mid level subsidence and dry air advection
behind this wave will then offer the potential for a clearing trend
late this afternoon into the evening. The circulation around sfc
high drifting toward the mid Atlantic early Sat morning may however
allow some remnant low clouds to funnel back across Se Mi under a
deepening low level inversion. Despite indications of this in the
latest hi res models, confidence is not yet high enough to carry an
overcast low cloud deck in the TAFs late tonight through Sat
morning.

For DTW...There will be a gradual weakening of the northwest winds
this afternoon while they slowly back toward the west. This will be
a result of the high pressure system expanding into the Ohio Valley
and the corresponding weakening of the sfc gradient.

/DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 ft this afternoon. Low this evening
  through the day Saturday.

&&

.PREV DISCUSSION...
Issued at 1011 AM EST Fri Feb 16 2018

UPDATE...

As of 1010 AM EST...Current forecast largely in good shape with just
some minor tweaks regarding the timing of the breaking up of clouds
this afternoon. Regional observations and satellite this morning
continue to indicate plentiful stratus deck across much of the
region, with the exception being some partial clearing reaching into
portions of the Saginaw Valley. Forecast soundings continue to reveal
that this shallow boundary layer moisture remains trapped under a
strengthening subsidence inversion, that will initially be aided by
diurnal heating heading into the early afternoon. However, building
high pressure and increasing dry air noted upstream will continue to
advect southeastward into lower Michigan as the afternoon progresses,
with dry air entrainment processes at the boundary layer capping
inversion finally eroding cloud cover rapidly by early evening. A few
light snow showers across the northern lower peninsula will struggle
to make it too far south, so expecting a dry day across the region.
Temperatures will be cooler than yesterday, generally in the 30s.
With a brisk northwest wind, wind chills will bring a nip to the air
with values as cold as the upper single digits at times.

PREV DISCUSSION...
Issued at 241 AM EST Fri Feb 16 2018

DISCUSSION...

A cold frontal boundary will continue to sag south of the area today
as high pressure builds quickly eastward into the southern Great
Lakes and Ohio Valley. Cooler conditions can be expected today into
Saturday as this feature builds across the region. High temperatures
will generally range in the 30s both days with low temperatures in
the teens for most locations early Saturday morning. This high will
also bring a period of quiet weather into Saturday.

The next chance of precipitation will come late Saturday into
Saturday night as a shortwave disturbance, now coming onshore over
British Columbia, races through the region within rather progressive
upper level flow. A second notable shortwave disturbance within the
subtropical jet stream will lift from near Baja California into Ohio
Valley during the same time frame. At this time, the consensus of
model runs suggest these features will not phase with each other.
That will keep heavier rainfall to the south of the area with the
southern wave while a period of light snow showers shifts through
lower Michigan with the northern stream wave. Accumulations, if any,
still appear to be insignificant.

A large shift in the upper level pattern is then expected to take
shape from late this weekend into the first part of next week as
upper troughing builds into the western CONUS and upper ridging
expands over much of the CONUS east of the Mississippi Valley. The
developing southwesterly flow regime will lead to milder readings by
Sunday with high temperatures climbing back into the 40s.

From late Sunday night into Tuesday, several shortwaves (and related
low pressure systems) are forecast to eject northeastward from this
building upper trough into the upper midwest/western Great Lakes.
Current positioning of the mean upper trough/ridge pattern suggests
these disturbances will track west of the region and keep Southeast
Lower Michigan within the warm sector. This will bring widespread
50s to the forecast both Monday and Tuesday with a very good chance
at precipitation (mainly rainfall) as a substantial amount of
moisture is pulled northeast into the area within this pattern. Will
even maintain a mention of thunder on Tuesday as elevated stability
levels decrease with this influx of moist/mild air.

From Wednesday on, the western CONUS upper trough gradually expands
eastward to cover more of NOAM. This will bring a cooling trend from
mid to late next week with drier conditions also settling back into
the region. Highs by Wednesday/Thursday will settle back into the
30s to around 40 with lows in the 20s.

MARINE...

Cold air advection has begun in the wake of the Thursday evening
cold front. A second surge of colder air will occur this morning
which will keep northwesterly winds elevated through the afternoon.
There will be a brief period where gusts could exceed 30 knots
today. Winds will then back to more westerly while decreasing this
afternoon as high pressure begins building across the southern Great
Lakes. This will result in a lull in the winds until Saturday when
the high drifts off to the east bringing southwesterly flow back
across the region in advance of the next cold front. Winds will once
again gust to near 30 knots Saturday afternoon into the evening
hours.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SC
UPDATE.......IRL
DISCUSSION...DG
MARINE.......DRK


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