Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 171754
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
154 PM EDT Tue Apr 17 2018

.UPDATE...
Issued at 1147 AM EDT Tue Apr 17 2018

12z surface/composite analysis shows a broadening area of low
pressure straddling the Ontario/Quebec border (~997mb)...surface
trough trailing back to the west across the Straits of Mackinac.
Deep layer cyclonic flow continues to wrap back across the upper
Great Lakes...with a couple of disturbances rotating around the
parent low. One vorticity center was just exiting northeast Lower
and taking what should be the last batch of widespread snow along
with it...a second vorticity center clearly seen in IR imagery
dropping south along the eastern shore of Lake Superior...combined
with lingering isentropic ascent is still producing some light
snow/flurries that are spreading into eastern Upper. Marginally
cold enough for a little lake contribution.

Looks like things will finally settle down across northern
Michigan after 3+ days of off-season winter mayhem. Secondary
vorticity center should at least clip eastern Upper/far northeast
Lower this afternoon...will keep skies cloudy but additional
precipitation should be light/minimal. Afternoon highs should
reach the lower-mid 30s...many locales have already warmed at or
above 30 degrees.

&&

.NEAR TERM...(Today through Tonight)
Issued at 328 AM EDT Tue Apr 17 2018

...Winter to relax its grip a bit...

High impact weather potential: ongoing snow diminishing early
today.

998mb surface low is a bit ne of Georgian Bay, a reflection of a
broad/deep 500mb low over the northern and eastern Great Lakes.
These systems will slowly move down the St Lawrence Vly thru
tonight, and the deepest moisture will also be departing eastward.
However, there is no push of actual dry air into the region, and we
remain beneath deep cyclonic flow until very late tonight. Toward
Wed morning, the arrival of a shortwave ridge in the western lakes
will (briefly) provide somewhat better drying. Precip/cloud trends
are the main concerns.

Presently, best snowfall is found over eastern upper and far
northern lower MI, with a lobe rotating back into the advisory
area in nw lower MI. Near-term models are in agreement that this
lobe will essentially be the last of the synoptic snow with this
event. By 12z/8am, snowfall will just be hugging the ne lower MI
coast, along with some light lake effect over nw lower and eastern
upper MI. Accums before 8 am will be an inch or less. Plan on
leaving the ongoing advisory up thru the current expiration of 5
am, and not extending.

Inversion heights will sharply lower as we move thru the morning,
and will settle below 850mb/3k ft by noon. There is a corresponding
decrease in overlake instability, which is already a bit on the
marginal side (850mb temps rising to -8/-10C). Snow shower
coverage will be reasonably high to start the morning in
snowbelts, but will decrease as we move thru the morning hours.
Expect only sct activity at most this afternoon. Accums after 8
am less than inch. Though little precip is expected outside of the
nw flow snowbelts this afternoon, cloud cover is expected be to
extensive.

As 1000-850mb winds weaken and veer northerly tonight, we will see
any snow showers end, and a decrease in cloud cover, especially
in eastern upper/ne lower MI. Otherwise little wx of note.
Guidance is not inclined to decouple surface winds, which should
keep min temps from tumbling too drastically (despite huge amounts
of fresh snow cover). Note that any tendency for lighter winds
could lead to sharply colder temps tonight, especially north of
M-32.

Max temps in the 30s. Min temps in the 20s.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 328 AM EDT Tue Apr 17 2018

...Weak system moves through late Wednesday, Early Thursday...

High Impact Weather Potential...It is possible for freezing
drizzle/rain Wednesday night before becoming all snow and ending.

Pattern Synopsis/Forecast...Wednesday morning the sfc high moves out
of the the forecast area, allowing the sfc low to move into northern
Indiana and the 500 mb low into N Illinois by 00z/Thu. GFS and ECMWF
have the precipitation moving into the forecast area, south of M-72
and west of I-75. The models then diverge solutions with the ECMWF
keeping the low on a more southerly track than the GFS, and without
a lot of moisture in the 700-500 mb layer. The dry air in the mid
levels (which the GFS has when you look at the model sounding) is
the problematic portion of this and will be discussed in the
forecast concerns section.

However, by Thursday morning the models are showing the upper level
lows moving east, and beginning to pull the moisture out of the
region while the GFS lags a bit, not leaving the region until
00z/Fri. Thursday night (through 12z/Fri), the high pressure then
takes control and the dry air begins to clear things out.

Primary Forecast Concerns...The Question for the forecast is whether
there will freezing rain/drizzle? At this point, based on the qpf,
there will be mostly drizzle, but my best guess is that it will be
patchy as models have a lot of mid level dry air that may cause
issues allowing the moisture to coalesce at time. Also, the ECMWF
doesn`t allow precipitation north of M-32. Think that the ECMWf may
be onto something as the sfc high moves into Hudson Bay, it will
pump more dry air into the region, especially looking at the 850-700
mb layer. If this is the case, the moisture may be more confined
even lower in the boundary layer, so that the moisture would just
"spit" some instead of really drizzle all night. The latest NAM and
HiRes would side with the ECMWF, while the SREF is on board with the
GFS. Considering the time of year, the drier air from a Hudson Bay
High would be a strong deterrent for the moisture.

.LONG TERM...(Thursday night through Monday)
Issued at 328 AM EDT Tue Apr 17 2018

...Precipitation Free Weather and Moderating Temperatures...

Extended (Friday through Monday)...The models dry things out through
the weekend, as High pressure builds into the Upper Great Lakes at
the sfc and aloft. Lots of dry air pushes into the region as a
result and the 500 mb heights begin to build. This pushes our
temperatures up from the mid 40s on Friday to the mid 50s on Monday.
It would be surprising if, with the sunshine that one would expect
with this pattern that we could get back to the normal high
temperatures for this time of year which are the mid to upper 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 153 PM EDT Tue Apr 17 2018

Anticipating MVFR ceilings to persist through the night...with
little additional precipitation. May see some improvement in
ceilings possible toward midday Wednesday.

&&

.MARINE...
Issued at 328 AM EDT Tue Apr 17 2018

Brisk nw winds will persist today, especially early, before winds
veer more northerly and weaken into tonight as low pressure moves
further away to the ne. Advisories remain in order for today on
all waters.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 5 PM EDT this afternoon for LHZ347-
     348.
LM...SMALL CRAFT ADVISORY until 5 PM EDT this afternoon for LMZ323-
     342-344>346.
LS...SMALL CRAFT ADVISORY until 5 PM EDT this afternoon for LSZ321-
     322.
&&

$$

UPDATE...JPB
NEAR TERM...JZ
SHORT TERM...JL
LONG TERM...JL
AVIATION...JPB
MARINE...JZ



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