Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 190427
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1127 PM EST Sun Feb 18 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Sun Feb 18 2018

A period of wet weather and warm temperatures are expected beginning
later tonight, and lasting into Wednesday. Periods of rain with some
thunderstorms are expected. Rainfall of 1 to 3 inches is expected,
with some locally higher amounts possible. The rain will change over
to some mixed precipitation late Tuesday night and Wednesday as
colder air pushes in.

There will be small chances of precipitation for the end of the
week, with additional chances next weekend. Overall, temperatures
are expected to remain generally above average through the period.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EST Sun Feb 18 2018

We are issuing a Flood Watch for the entire area valid from noon
Monday through Wednesday with the forecast package this afternoon.
The reasons for this include the obvious 1-3 inches of rain
expected, the frozen ground which will limit ground absorption, and
up to around 2 inches of water in the snowpack (highest NW, less
SE). One thing that will limit the flood potential is the rain
coming over 36-48 hours. That said, there are still enough concerns
to justify the watch.

The general trend in the arrival of the rainfall has been delayed
slightly. Initial lighter rains will move in across far Southern
Lower toward daybreak, and then will spread across the remainder of
the area through Monday. This is when some of the better transport
initially moves in, and will set the stage for additional waves of
rain.

The frontal system that will be the focus for these waves of rain
will move into the NW counties later on Mon. This front will be
pushing into a very moist air mass by February standards where
Pwat`s will be up to around 1.3 inches,  or almost 3 times average
for this time of the year. The front will stall out for a bit as it
becomes parallel with the SW flow aloft. Short waves will ride along
the front and bring the waves of rain until Tue night when the
front starts to push SE.

We are fairly certain that 1 to 3 inches of rain is going to fall
over the area. The heavier rain looks to occur further SE where the
low level moisture axis will be maximized just ahead of the front.
There remains a concern that some locally heavier bands of rain
could fall with the waves and convection riding along the front.
This is difficult to pin point until almost as it is occurring as
the front will fluctuate with the passage of each wave. Areas up
across the NW look to see a little less rain. However they have more
water in the snowpack that will likely be released with the rain,
warm, and moist conditions. This is why we included them in the
Flood Watch.

Thunder will be possible beginning Mon afternoon, and will linger
until the front passes Tue night/ Wed morning. Instability is not
great, even in the warm sector where areas along and South of I-96
will likely see 60 on Tue.

We do see the potential for pcpn to transition from rain to snow
late Tue night and Wed morning as the colder air pushes in. There
could be a mix of all wintry pcpn as the colder air briefly
undercuts warmer air aloft.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EST Sun Feb 18 2018

A summer like Bermuda high is entrenched from Bermuda west through
Florida through the long term period. What this means for Lower
Michigan is a flat southwest flow aloft. The result in no cold air
intrusions between Wednesday and Sunday. In fact, 850mb temps
through that 5 day period do not vary much at all and remain within
a few degrees of zero Celsius.

The precipitation associated with the early/mid week rain event
should be exiting our area at midday on Wednesday. After that high
pressure should bring dry weather from Wednesday afternoon through
Thursday night.

There is a chance for a light mix of rain and snow from Friday into
Friday night, but this shortwave looks weak. Thinking we may
actually end up dry through much of these two forecast periods.

A better chance of precipitation (rain/snow) should come out over
the weekend from Saturday into Sunday as a stronger shortwave ejects
our way from the Western U.S. trough. Heating of the day will bring
mainly rain during the day with some snow mixing in overnight. Being
that it is 7 days out, the next weekend system has quite a bit of
spread in the deterministic models in terms of strength, depth and
track of a low through the Ohio Valley / Southern Great Lakes.

Bottom line the long term looks to be a decent time to allow the
rivers to recede with near to slightly above normal temperatures.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1115 PM EST Sun Feb 18 2018

VFR conditions will continue overnight before gradually
deteriorating to MVFR then IFR Monday morning as low clouds move
in and patchy fog develops. Conditions will deteriorate further
to LIFR Monday afternoon through Monday evening as very low cigs
develop along with areas of denser fog.

In addition scattered showers will develop and there is also
potential for some thunderstorms to develop by late afternoon
through the evening. Conditions should remain predominantly LIFR
through at least 06Z Tue.

&&

.HYDROLOGY...
Issued at 330 PM EST Sun Feb 18 2018

As a strong area of high pressure sets up over the Southeast U.S., a
solid stream of gulf moisture is expected to flow northward into the
Great Lakes. Guidance continues to suggest rainfall from Monday
through Wednesday with periods of heavy rain possible.

Widespread rainfall amounts ranging from 1 to 3 inches are expected,
with locally with excessive amounts of over 3 inches, especially
from Southwest Michigan to Saginaw Bay. Coupled with recent
snowmelt, a frozen ground, and continued high river levels, rainfall
will result in bankfull streams and rivers. Some locations are
looking at minor flooding, especially those immediately near and
adjacent to rivers.

A positive light in all of this is that temperatures in the 50s and
60s will reduce the presence of ice on rivers. High water flows are
likely to flush waterways, freeing up streams and preventing
immediate concern for ice jams, if temperatures were to return to
well below freezing territory in the future.

&&

.CLIMATE...
Issued at 330 PM EST Sun Feb 18 2018

Below are the high temp records, max low records, and precipitation
records for Mon, Tue, and Wed.

                 Mon 2/19    Tue 2/20       Wed 2/21

Muskegon
           High  58 (2017)   62 (2017)      58 (2017,1930)
        Max Low  44 (1994)   40 (1953)      41 (2017)
           Pcpn 0.88"(1994) 1.13"(2002)    1.44"(1997)

Grand Rapids
           High  62 (2017)   61 (1930)      66 (1930)
        Max Low  47 (1994)   50 (1930)      47 (1930)
           Pcpn 0.85"(1939) 1.40"(1898)    2.96"(1997)

Lansing
           High  62 (2017)   59 (2017,`83,`30) 62 (1930)
        Max Low  42 (1994)   42 (1930)         42 (2017)
           Pcpn 1.49"(1939) 1.04"(1891)       2.14"(1997)

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from Monday afternoon through Wednesday afternoon
     for MIZ037>040-043>046-050>052-056>059-064>067-071>074.

LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Duke
AVIATION...Laurens
HYDROLOGY...JAM
CLIMATE...NJJ



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