Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 192357
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
657 PM EST Mon Feb 19 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 314 PM EST Mon Feb 19 2018

A wet and warm period is expected from this evening through Tuesday
night. Periods of rainfall are expected through this time, with 1 to
3 inches of rainfall expected. Highest amounts are likely to be
found the further south you go toward the state border. Some locally
heavier amounts are likely. Flooding is likely, especially near
rivers and streams. Temperatures will warm into the 50s and lower
60s by Tuesday afternoon.

A front moving through on Wednesday morning will bring an end to the
rainfall. The precipitation could change over to some light snow
before ending. Colder air will move in behind the front for the end
of the week. Another system moving in over the weekend will bring
another chance of precipitation.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 314 PM EST Mon Feb 19 2018

No real changes are needed to the forecast this afternoon. The Flood
Watch will be left as is.

Initial batch of rain with this wet system has brought some rain to
much of the area, and is starting to exit to the east this
afternoon. This rain was the initial surge of moisture just out
ahead of the warm front that looks like it just crossed north into
Michigan as of 20z. It looks like we will see one break in the rain
through early this evening. A better batch of showers and embedded
thunder with a wave now over Il/MO has it`s sights set on Lower
Michigan this evening.

Once the warm front moves north of the area this evening, it will
remain nearly stationary into Tue night as it becomes parallel to
the SW upper flow that takes shape ahead of the long wave trough
approaching. This will allow additional short waves to ride through
the area. These short waves will be encountering precipitable water
values approaching 300% of normal for mid-late Feb.

The favored area for the heaviest rains remains S/SE Lower. We
continue to expect around an inch across our NW counties, to 3+
inches across our far southern counties. The widespread rainfall
alone across the south is enough to cause issues. When combining it
with some snow melt (more snowmelt to the NW), a frozen ground, and
high river levels coming into the event, brings a fairly high
likelihood of flooding on the rivers, and low lying areas.

Thunder chances remain, however instability remains fairly weak.
This will keep any severe chances low, even with temps
approaching 60 down south in the warm sector.

We will see the whole system get pushed east then on Wednesday
morning as the upper flow pushes it, and strong Canadian ridging at
the sfc pushes in. The frontal passage looks like it will be
accompanied by a brief change over from rain to snow before the pcpn
ends.

.LONG TERM...(Thursday through Monday)
Issued at 314 PM EST Mon Feb 19 2018

Main concern in the extended period will center around potential for
additional rainfall that could further aggravate flooding or slow
the receding of water.

High pressure will provide dry weather Thursday with high
temperatures warming to the mid 30s to low 40s, which is near to
slightly above normal. Upper energy ejecting out of the longwave
trough over the western U.S. will quickly slide over Michigan
towards the end of the work week, spreading what is more likely be
light precipitation into the area late Thursday night and Friday
morning. Thermal profiles are most suggestive of precipitation
starting as light snow late Thursday night before changing to rain
through the morning with the onset of daytime heating. Most models
suggest very light precipitation (both rain and snow) given weak
forcing and dry air that must first be overcome. 19.12Z GFS,
however, brings 0.25 to 0.50 inches of rain across far southern
Michigan, while the Euro and other solutions keep the heavier precip
south. Will continue to watch potential for the higher rain amount
scenario in the GFS, but follow the stronger consensus of the non-
GFS solutions.

Models then differ with when the next pieces of upper energy works
across the area, and whether the resultant round of precipitation
will occur on Saturday or Sunday. This should again be a mix of rain
and snow, with rain favored during the daytime. Amounts are hard to
judge given model differences with synoptic pattern, but another
prolonged heavy rain event is not expected.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 657 PM EST Mon Feb 19 2018

IFR and LIFR conditions expected to prevail through Tuesday
evening with bouts of steady rain. An isolated thunderstorm is
also possible but was left out of the forecast for now. LLWS will
also continue through Tuesday morning. Wind will be south to
southwest around 10 knots on Tuesday.

&&

.HYDROLOGY...
Issued at 314 PM EST Mon Feb 19 2018

A notable flood event is forecast to materialize over the next 48
hours. A combination of heavy rainfall, melting snow and frozen soil
is expected to lead to efficient runoff over the next couple days.
Flood conditions are expected to continue along streams and rivers
through the course of the week with some sites forecast to reach
moderate category and potentially higher.

Guidance continues to be rather persistent in painting a wide swath
of 1 to 3 inches in total rainfall across much of Lower Michigan.
The greatest potential to reach or exceed 3 inches will exist over
the southern one-third of the state. A few thunderstorms could be
embedded in the overall shield of rainfall, locally enhancing totals
tonight through early Wednesday.

All sites are affected by some form of a flood product,
incorporating information on river rises through the next several
days. While most sites rise to minor to moderate flood levels, few
sites are forecast to achieve benchmark levels. It is important to
note that any record forecast will be highly dependent on whether
forecast rainfall verifies and whether the extent of the modeled
snowpack truly includes the expected water equivalent. If rainfall
occurs as expected and rivers continues to rise, the rate of rise
will almost certainly slow with higher levels, as water continues to
spread out.

Residents and local officials should keep up-to-date with latest
forecasts and remain vigilant with regard to river levels over the
next several days.

&&

.CLIMATE...
Issued at 314 PM EST Mon Feb 19 2018

Below are the high temp records, max low records, and precipitation
records for today, 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 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...HLO
AVIATION...Ostuno
HYDROLOGY...JAM
CLIMATE...NJJ


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