Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 180443
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1143 PM EST Wed Jan 17 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 318 PM EST Wed Jan 17 2018

Fairly quiet weather is expected through the remainder of the work
week and for the first portion of the weekend. We are only expecting
intervals of clouds at times. Temperatures are expected to gradually
warm through the weekend, with a few 40s likely toward Saturday.

A strong storm system will begin to affect the area then by Sunday.
Precipitation chances will increase early on Sunday, with a short
mixture of precipitation types possible. Precipitation will change
over to all rain on Sunday and last through Monday with temperatures
in the 40s.

Colder air will surge back into the area by Tuesday as the storm
system passes through the area. Some snow showers will become
possible at that time.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 318 PM EST Wed Jan 17 2018

Not much to discuss in the short term, especially by mid-January
standards. Upper ridge building over the area today has dried
conditions out over the area, except for some mid clouds floating
through. Tight gradient between low in Canada, and strong high
approaching the lower Mississippi River Valley is bringing some
breezy conditions to the area, which is advecting in warmer temps
compared to the last couple of days.

We do see a strong short wave/low across Saskatchewan this afternoon
that will make its way toward Nrn Michigan on Thursday. This is
expected to open up a bit before it arrives. We do not expect pcpn
with this wave as the majority of the forcing with the wave remains
just North of the area, and moisture is fairly anemic with the DGZ
unsaturated. This will bring a brief pool of low level cooler air
for a short period. Essentially it will limit the amount of warming
that takes place instead of cooling us down.

Upper ridging will then move back in by Fri, and will be suppressed
a bit for Fri night with upper lows over Canada. This will keep the
area dry through Fri night, with temperatures gradually moderating.

.LONG TERM...(Saturday through Wednesday)
Issued at 318 PM EST Wed Jan 17 2018

It would seem to this forecaster that the next seven days (running 7
day mean of the daily average temperature) is likely to be one of
the warmest 7 day periods of the month of January (through the 31 of
January, using ensemble model forecast to finish the month). We
should average between 5 and 7 degrees above normal. I do have to
point out we do get colder once again in the Tue to Wed time frame.
Even so this will be one of the warmest weeks of the month.

The other story is the potential for heavy rainfall in the Sunday
night into Monday time frame. This system has excellent overall
continuity and has been in the model forecasts since the  of
January. This system seems like it will be more phased than the one
that gave us record highs on the 11th, so it will likely be deeper
and have more surface winds.  Being more wrapped up, it will pull
down more cold air and have a decent lake snow event behind it and
at this point it would be a more westerly event than the mostly
northerly type events we have since since mid December.

The big picture shows our La Nina has developed to the point that
nearly all the significant convection over the north and central
Pacific Ocean is now west of 120E.  That has not been true over the
north Pacific in several years. Likely it is the result of cooler
water over the eastern Pacific and significantly warmer than normal
water near Asia. This is also leading to a retraction of the East
Asian Jet, which is at least part of the reason we will cool off
again, by the middle of next week. Another aspect of this is there
is an omega block over the western Pacific, that is causing system
over the Gulf of Alaska to stall there, which leads to a building
ridge over western North America. Once again allowing cooling for us
by the middle of next week. Meanwhile through, as the next strong
Pacific system moves through the western United States late this
week, into the weekend, our next storm redevelops over southern
Plains system by Saturday. That system will track trough our area
Monday with heavy band of rain ahead of the cold front, likely early
to mid morning Monday. All the southerly flow ahead of that system
in conjunction with the polar jet being located in Canada for the
next 5 days, leads to warmer surface temperatures here. Then the
cold air surges in behind the system Monday night into Tuesday and
that sets up lake effect snow showers into Wednesday.

We will have to monitor our rivers for ice jams but the good news
there is it will be a slow warm up, and there is a limited amount of
snow on the ground, meaning snow melt will not add a lot of water to
our rivers (mostly less than a 1/2 inch of water in the snow pack
over the CWA).

Bottom line is warmer Sat into Monday, then very wet Monday,
followed by colder and lake effect snow showers into Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1112 PM EST Wed Jan 17 2018

VFR conditions will continue at most of the terminals through the
next 24 hrs. However a brief period of MVFR is possible overnight
into Thursday morning due to some low cloud development. Otherwise
VFR will prevail thru Thursday evening.

Breezy conditions will persist overnight through Thursday with
southwest winds of 15 to 20 kts and frequent gusts to around 25
kts. Wind speeds will finally subside a bit Thursday evening.

&&

.HYDROLOGY...
Issued at 318 PM EST Wed Jan 17 2018

Slight improvement has been noted on the Muskegon River in Mecosta
County. Water levels have receded by approximately 6 to 12 inches.
Resulting impacts are relatively similar to when they were first
reported Monday evening. Residents along the river are not out of
the woods yet, but recent decline in levels signals enough that
volume of water is making it under the ice to allow conditions to
slowly improve.

The combination of warmer temperatures and precipitation over the
weekend into early next week continues to be a concern. Guidance is
rather persistent in pushing near/above 40 degree temperatures into
Lower Michigan Friday through Monday. NOHRSC (National Operational
Hydrologic Remote Sensing) estimates show aerial averages of around
0.50" liquid equivalent in the current snowpack with highest amounts
distributed south and east of Grand Rapids. Precipitation totals are
forecast to be 0.50" over Southern Lower Michigan to more than 1.00"
over West-Central Lower Michigan through early next week.

Flood potential could increase through the weekend, especially early
next week, as temperatures and runoff impacts rivers.

&&

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

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...WDM
AVIATION...Laurens
HYDROLOGY...JAM



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