Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 170758
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
258 AM EST Sat Feb 17 2018

.DISCUSSION...

A weak shortwave will cross the area quickly this evening with a
brief period of light snow showers or flurries possible. At this
time, it appears snowfall accumulations will be insignificant (a
dusting or less in most locations). Another shortwave within the sub-
tropical jet stream is still forecast to remain well south of the
area during this time frame, focusing heavier/more widespread rain
over the Tennessee Valley.

Once this shortwave races off to the east coast, upper ridging will
begin to build across the eastern CONUS as a large upper trough digs
into the western CONUS. This pattern shift is expected to lead to a
period of very mild and wet weather from very late Sunday night on
through Monday into Tuesday/Tuesday night (and perhaps into parts of
Wednesday.

While the weather will remain dry through Sunday, the building ridge
will already lead to moderating temperatures with highs reaching the
40s in many locations during the afternoon. Several shortwaves will
then eject northeast into the area from the expanding upper trough
to the west and provide numerous waves of rain during the first half
of next week.

The first of these will bring precipitation to the area very late
Sunday night into Monday. Most (or all) of this precipitation will
fall in the form of rain as temperatures climb steadily into the mid
30s by the time this moisture arrives over the area in the 09z-15z
time frame Monday morning. While models are rather inconsistent in
the exact placement of best FGEN forcing (and hence, heavier bands
of rainfall), all agree in a very good chance of rainfall with an
increasing chance into Monday afternoon/night. Local rainfall
amounts with this first impulse could very well top half an inch in
some locations.

Additional shortwave energy then lifts into the region Tuesday into
Tuesday night. The upper trough/ridge configuration still suggests
the surface low pressure system associated with this system will
lift into the central Great Lakes just to the west of Southeast
Lower Michigan. This puts the area well within the warm sector and
anticipate temperatures will remain in the 40s and 50s across most
of the area Monday night with highs climbing into the 50s and 60s on
Tuesday.

It is during this period that the best chance of heavy rain and
embedded thunderstorms will exist with local rainfall amounts of an
additional inch quite possible. All told, some areas may receive 2+
inches of rain from Monday into Tuesday evening. While significant
flooding is not anticipated, the combination of this widespread
rainfall and continued snow melt will certainly lead to some minor
issues across the area. In addition, the mild temperatures will
increase the probability of ice on area streams/rivers breaking up
to some degree, potentially exacerbating local flooding concerns.

The aforementioned upper trough over the west will then flatten
somewhat and expand east across northern NOAM. While the period of
heavy precipitation will likely shift east of the area Tuesday
night, additional rain (and possibly snow) will linger into
Wednesday this upper level feature expands across the region.

Overall, temperatures will settle back into the 30s/40s during the
last half of the week after the very mild period from Monday into
Tuesday evening. Some moderation will be possible into next weekend
as the next shot of precipitation shift back east/northeast into the
region.

&&

.MARINE...

Southwesterly winds will increase into the afternoon hours as the
gradient tightens in advance of an approaching cold front. Wind
gusts will peak around 30 knots through the early evening with
higher gust potential being tempered by extensive ice cover. Winds
will veer to the west-northwest in the wake of the cold front
Saturday night but will quickly flip back to the south on Sunday as
a warm front lifts up through the Great Lakes. Winds will again
approach 30 knots Sunday evening.

&&

.HYDROLOGY...

There is high probability of a substantial warming trend Monday into
Tuesday, resulting in a complete melt off of all snow cover across
Southeast Michigan. This warming will occur as a result of strong
southerly flow ahead of a slow moving front. In addition, periods of
rain are expected along this front, beginning Monday and possibly
persisting into Wednesday. Forecast confidence on how quickly this
system moves east of the region and where the axis of heaviest rain
will fall still carries a good deal of uncertainty. There is however
a chance that total rainfall amounts from Monday into Tuesday night
will reach two inches in some locations. While the complete melt of
snow will not be enough to support flooding, the potential rainfall
with the snow melt will lead to a chance for significant rises on
area rivers and streams. The mild weather will also lead to some
break up of ice on area rivers and streams perhaps exacerbating
issues in some locales.

&&

.CLIMATE...

Record high temperatures will be possible across much of southeast
Michigan Tuesday. Here is a look at record high temperatures for
Tuesday, February 20th:

Detroit                63 (set in 2016)
Flint                  61 (set in 1930)
Saginaw/Tri-Cities     62 (set in 1930)


&&

.PREV DISCUSSION...
Issued at 1151 PM EST Fri Feb 16 2018

AVIATION...

A period of dry and stable low level conditions heading into the
early morning period, while a pocket of higher moisture looms just
to the south. Recent satellite trends and model guidance continues
to support a clear sky holding across the lowest 10 kft during the
latter half of the night. Developing light southerly flow will then
work to draw the upstream moisture back into southeast Michigan mid-
late morning Saturday. Still a mixed signal as to possible coverage
and duration, but confidence is high enough to provide a definitive
mention. Ceiling height expected within the 2500 to 3500 ft range.
Brief shot for light snow showers Saturday evening with a cold
frontal, with limited impact given the small duration window and
lack of greater forcing.

For DTW...Clear skies hold across the lowest 5000 ft through the
latter half of the night. Increasing potential for cigs to fall
below 5000 ft Saturday morning /onset 11z-13z/, as moisture now over
northern Indiana attempts to lift back into the region.

/DTW THRESHOLD PROBABILITIES...

* Low for cigs below 5000 ft tonight. Medium on Saturday.

* High for ptype as snow Saturday evening.


&&

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

$$

DISCUSSION...DG
MARINE.......DRK
HYDROLOGY....DRK
CLIMATE......DG
AVIATION.....MR


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at www.weather.gov/detroit.



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