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Area forecast discussion 
National Weather Service Grand Rapids Michigan
1125 am EST Sat Dec 20 2014

Latest update...
update

Synopsis...
issued at 329 am EST Sat Dec 20 2014

Quiet and mild weather is expected for the area through the first
part of the day on Monday. Clouds will generally be on the increase
with mainly dry conditions expected into early Monday. A weather
system will begin to impact the area Monday afternoon by bringing
rain into the area.

The weather will become more unsettled leading up to the Christmas
Holiday on Thursday. Rain will affect the area off and on from
Monday night into Christmas evening before rain changes to snow
Christmas day.

&&

Update...
issued at 1120 am EST Sat Dec 20 2014

Made small tweaks to the temperatures and cloud cover for this
afternoon...but overall forecast is on track. High temperatures
should climb into the lower 30s in most areas.

Cloud trends were the main item of concern. Lower clouds are
currently situated across the western portion of the forecast area
towards Lake Michigan and over the southeast towards Jackson.
Winds at 925mb/S will be light (5-10 knots) from the west-
southwest this afternoon...so expecting that the clouds will
slowly slide to the east. By 700pm this evening most areas should
have the low clouds in place with the exception being the far
northeast up toward Montana. Pleasant and Clare.

&&

Short term...(today through monday)
issued at 329 am EST Sat Dec 20 2014

The main challenges in the short term portion of the forecast through
Monday are cloud trends initially...then precipitation trends for the later
portion of the period.

Low clouds have generally remained west and south of the area thus
far this morning...while high clouds are moving overhead. The high
clouds are streaming in ahead of the wave that is diving south of
the state. Low clouds cleared most of the area yesterday...and have
not moved much with the weak flow in place. We are expecting the low
clouds to spread in over at least a portion of the area later today
and tonight as the flow brings them back in across the area.

We will see periods of clouds at different layers then through most
of Sun night. The low clouds will remain around the area...and some
middle/high level cloud cover will move over as warmth and moisture
aloft advects over the area.

We will not see much of a chance of precipitation through early Monday. The only
real chance will come late Sun afternoon and sun evening across the far
northwest corner of the County warning forecast area where some light snow will be possible. We
will see a warm front push north through the area at that time. The
best moisture transport will occur northwest of the area and this is where
the deepest moisture will be found. Once the front passes by 12z
Monday...we could actually see some temporary clearing.

The threat of rain will then increase later on Monday from west to east
as the initial upper wave and associated surface low approach the area.
The atmosphere will have warmed sufficiently by the time precipitation moves
in that all precipitation should be rain. We will see temperatures into the 40s on
Monday ahead of the initial front.

Long term...(monday night through friday)
issued at 329 am EST Sat Dec 20 2014

Although an impressive low will be moving through or close to the
forecast area next week...impacts may not amount to much. For now it
looks like snow totals will not be heavy as the cold air is late to
wrap in and lake effect will not add much. A few hours of strong
winds from this so called Santa bomb could be the only threat.

The 00z model guidance is narrowing in on the timing for the change
from liquid to frozen precipitation. Looks like cold air moves in from
southwest to northeast on Wednesday afternoon with snow amounts
generally under 4 inches. Then some lake effect follows for Thursday
but should not be heavy as inversion heights remain at or below 5 kft.

Next storm end of the week is low confidence with high model spread.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 645 am EST Sat Dec 20 2014

Thin stratus deck with ceilings 2200 to 3000 feet above ground level and light
fog will bring patchy MVFR conditions across lower Michigan today
and tonight. Winds will be light from the southeast.



&&

Marine...
issued at 339 PM EST Friday Dec 19 2014

High pressure will bring fairly light winds and low wave action
tonight into Saturday. Southerly flow begins to pick up on Sunday.
Small Craft Advisory conditions may develop as early as Sunday
afternoon in the north. Sunday night it appears Small Craft Advisory conditions will
be likely...north of Holland. Will hold off at this point on a
fourth period Small Craft Advisory...but one will likely be needed going forward.
Next week looks rough on Lake Michigan given a deep low moving
through the region.



&&

Hydrology...
issued at 339 PM EST Friday Dec 19 2014

River levels across the area are near normal for this time of year
with no significant precipitation expected through the weekend. So...no
Hydro issues through Monday. Deep low pressure will likely bring
soaking rains to the area Monday night into Tuesday with rainfall
amounts of a half to one inch. Given the low flows currently this
should be able to be absorbed without much issue.

&&

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

$$

Update...Duke
synopsis...njj
short term...njj
long term...ostuno
aviation...ostuno
hydrology...Duke
marine...Duke

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