Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 132018 CCA
AFDGRR

Area Forecast Discussion...CORRECTED
National Weather Service Grand Rapids MI
318 PM EST Tue Feb 13 2018

LATEST UPDATE...
Synopsis/Short Term/Long Term

.SYNOPSIS...
Issued at 310 PM EST Tue Feb 13 2018

After nearly 2 weeks of below normal temperatures it is time for a
warm up. The combination of a departing high pressure system and
system coming out of the southern Rockies will provide warming
southwest winds into Thursday. As the systems passes south of
Michigan Thursday, we may get some rain showers in the afternoon.
Then a Canadian cold front merges with that system from the
southern Rockies Thursday afternoon as it moves east along I-80 in
the afternoon. Once east of us, the cold air comes back for
Friday and Saturday. Than a more prolonged warm up with a
significant amount of rain begins Sunday. As the warmer air comes
in there may be a little snow mixed with the rain at first. Then a
stationary front develops over the area and waves of low pressure
ride along the front into at least Wednesday. This could result
in a soaking rain. Temperatures may well rise well into the 50s
early next week too before the cold air comes back later in the
week.


&&

.SHORT TERM...(This evening through Thursday night)
Issued at 310 PM EST Tue Feb 13 2018

The main issue I see is how quickly does the low clouds and
drizzle come into our area. The persistent southerly flow head of
the system coming out of the southern Rockies is what will bring
the low clouds and drizzle into our area by tomorrow evening.
The low clouds, fog and drizzle are the result of that system
tracking east northeast of of the southern Rockies, on the
southern branch of the polar jet. There is significant 1000 to
850 moisture low level moisture transport ahead of the system and
the lead edge moisture field could reach Southwest Michigan by
tomorrow afternoon or evening. At that point there is not deep
moisture in place, so more than likely we will see low cloud, fog
and drizzle Thursday morning. As the system passes south of us
there is enough dynamics to bring in mid clouds so we more than
likely will see afternoon rain showers.

The cold air does not come back until the deep moisture is gone
and that will be after midnight Thursday, or actually early Friday
morning. So Thursday night we will see showers mix with and
change to snow showers, mostly after midnight. No significant
snowfall is expected from this.



.LONG TERM...(Friday through Tuesday)
Issued at 310 PM EST Tue Feb 13 2018

We will see a brief cool down Fri into Saturday before the real
warm up begins. This is likely to cause a significant amount of
rain early next week,it will be much to warm to even think about
snow. The rain to snow line early next week may be near or north
of Lake Superior. This deep western trough will send a series of
waves along a nearly stationary front, which will likely be close
to us into Wednesday. Each wave on the front will give us rain.
The main wave, that will kick all of this east of us may not come
out of the western trough till Wed or even after that.

The real warm up happens because a system currently coming of
Korea, breaks through the upper ridge over the eastern Pacific
Ocean than merges with a northern stream shortwave causing the
western trough to deepen . That in turn builds a large eastern
ridge but the center of that ridge is over the Atlantic Ocean so
we will be near the storm track early next week. There has been
good agreement over the past 5 days or so that most of the really
heavy rain will be in the Tennessee and Ohio Valley area but we
will be close enough to moisture from all of this so that will
will have to watch this closely. The models have wavered over the
past few days just exactly how close to us these front waves get
but no matter they will be close enough to us that this will
remain an issue.

As the warm air comes back in Sunday we may see a period of mixed
rain and snow (precipitation amount Sunday will be less than a
tenth of inch). There may even be some freezing rain or drizzle
too. By Sunday night or Monday the first of several frontal waves
moves up the front bringing above freezing temperatures and rain
to the area. Several more waves on the front are expected but this
far out timing is an issue. Seems the cold air does not really
come back until at least Thursday of next week, and that may be to
soon.

It should be noted that I believe the official forecast I created
for Sunday night and Monday is significantly colder than what I
really believe will happen. The forecast is like it is for
continuity issues.



&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1218 PM EST Tue Feb 13 2018

The area of mid and high clouds will depart by late this afternoon
leaving mostly clear to clear skies through the night. However a
strong southwest flow develops just above the surface so I have
added LLWS to all of our TAFs overnight.

The glitch for tomorrow is if and went the low clouds (IFR
ceiling) move in. Most of the models show enough low level
moisture returning Wednesday so as to allow for a cloud deck with
bases near or below 1000 ft moving in from the south during the
afternoon or early evening. This will have to be watched as it
may come in as early as 12z at the I-94 taf sites.


&&

.HYDROLOGY...
Issued at 1101 AM EST Tue Feb 13 2018

A warm up this week and up to a quarter inch of rain Thursday should
result in melting snow and ice, and rising river levels. This could
also result in shifting ice and additional ice jam formation.

A flood advisory remains in effect for the Looking Glass River near
Eagle due to elevated levels of water/ice from an ice jam. River
levels in the vicinity of ice jams will continue to fluctuate by
several feet until the ice breaks free.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...WDM
AVIATION...WDM
HYDROLOGY...63



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