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fxus63 kgrr 231753 
afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
1253 PM EST Tue Jan 23 2018

Latest update...
aviation

Synopsis...
issued at 257 am EST Tue Jan 23 2018

A low pressure system will track northeastward through Michigan
today. Colder air will be drawn into this storm as it pulls
through. This will result in any remaining rain transitioning to
snow today. A broad area of high pressure will then build in from
the west for Wednesday before heading east of the area on
Thursday. This system will provide the region with mainly dry
weather.

&&

Update...
issued at 1107 am EST Tue Jan 23 2018

Forecast remains on track as all areas have now changed over to
snow. Accums will remain limited and it will be a wet snow, with
roads largely remaining wet. Accums will be around an inch across
the northern row of counties and also toward the lake north of
Holland, where the snow should get a slight boost off the moisture
from the lake. Elsewhere accums will remain under an inch.

Temps will remain steady in the lower 30s to around 30 much of
the day, then fall into the 20s by late afternoon.

Update issued at 712 am EST Tue Jan 23 2018

The transition to snow was a little quicker...especially toward
Ludington where the temperature is already below freezing. Based
on that plus radar showing an organized band tracking through I
updated the forecast and also issued an Special Weather Statement. Local 2 inches
possible near the points. Will be monitoring the remainder of the
Lakeshore for possible Special Weather Statement issuance's.

&&

Short term...(today through thursday)
issued at 257 am EST Tue Jan 23 2018

The main challenge in the short term deals with the coverage and
type of precipitation today. One organized area of rain and snow
was located around North Chicago to Milwaukee and heading east. A
second area was in central Illinois and central Indiana and was
tracking northeast. These areas of precipitation were associated
with a rather deep upper low...with a trowal supporting the first
batch of precipitation an a vigorous mid level vort enhancing the
second. Based on the trends...the high res models show the first
area of precipitation moving into southwest parts of my County Warning Area this
morning with the second area continuing to build
northeast...heading into my southeast County Warning Area. Will feature highest
pops for these locations mainly this morning. As for the
type...observation trends suggest the changeover to snow is
happening quicker than forecasted by the models. I made some
changes to the grids to show this sooner trend. We may struggle to
get surface temperatures down below freezing to start the
day...which is when most of the precipitation falls. Thus any
impacts at this point are forecasted to be minor. Will need to
monitor this closely though given the better lift and deeper
moisture that will be around.

The rest of the forecast looks rather quiet with temperatures
settling in to values closer to what we would normally see this
time of the year.

Long term...(thursday night through monday)
issued at 257 am EST Tue Jan 23 2018

Low pressure moving across Ontario will drag a cold front through
Michigan Saturday. The ECMWF is a bit slower than the GFS and
develops a wave on the front that then rides north across the cwa.
As such the ECMWF is the wetter solution. This pcpn will likely be
rain as temps will be well above normal Friday and Saturday...in the
mid 40s. The trailing upper trough will migrate across the state
Sunday/Sunday night and is much deeper and slower on the ECMWF than
the GFS. Due to the model differences, confidence in pcpn timing and
quantitative precipitation forecast if low. Cooler temps will move over the cwa Monday as the trough
moves by, but highs will be close to normal.

&&

Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1252 PM EST Tue Jan 23 2018

A band of snow is working through the taf sites at 18z.
Visibilities are in the 3 to 5 mile range within the band with the
possibility of brief dips in visibility to around 1 mile. Klan
stands the best chance at seeing the lowest visibilities. The snow
was weakening though and is shifting fairly rapidly to the east.
By 20z, the heavier snow is expected to be over with. During the
late afternoon hours, 20z to 00z, some flurries can be expected
but overall visibilities should be VFR.

Ceilings the next 24 hours look to be solidly in the 1000-2000ft
range. As we move into Wednesday, ceilings may try to rise into
the 2000-3000ft layer.

Winds will be gusty from the west-northwest (280-300 degrees)
this afternoon in the 15-30 knot range. Winds will diminish
considerably to below 10 knots this evening between 01z and 04z.

&&

Hydrology...
issued at 330 PM EST Monday Jan 22 2018

Snow has melted or nearly melted across west Michigan as of Monday
afternoon. Rain that fell across the area last night and this
morning averaged between 0.25 and 0.5 inches along and south of a
line from South Haven to Mason, and between 0.5 and 0.9 inches to
the north of there. Additional rainfall today is expected to be
lighter, with most areas receiving less than an tenth of an inch of
rainfall.

Additional precipitation is expected tonight and early Tuesday on
the backside of low pressure tracking through the area. The heaviest
amounts of precipitation, a combination of rain and melted snow,
through Tuesday afternoon would be most likely to occur over
portions of central Michigan. Amounts are not expected to be heavy
enough to cause additional flooding, but potential for ice jams will
still exist as river levels rise. A relatively dry stretch of
weather is then expected Tuesday night through Friday.

Rises on many rivers across the area are already being observed as
water runs off the frozen ground. Some of the slower responding
rivers will continue to see these rises continue through the end of
the week. The only river Flood Warning in effect as of Monday
afternoon was for the Looking Glass river near Eagle. Sycamore Creek
near Holt may near warning criteria, and the advisory could need to
be upgraded later this evening. The Portage River near Vicksburg is
the only other river that could exceed flood stage by Tuesday night.
Numerous river flood advisories are in effect. Please see the latest
flood advisory statement for more information. The rainfall and
warmer temperatures (both today and late this week) will aid in the
breakup of river ice, and will continue to provide concern for ice
jams. The most likely impacts from these would be minor flooding
upstream of the ice jam.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...none.
&&

$$

Update...jk
synopsis...mjs

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