Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 140103
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
903 PM EDT Fri Apr 13 2018

.UPDATE...
Issued at 900 PM EDT Fri Apr 13 2018

...All headlines will remain unchanged...

One really challenging forecast for the remainder of tonight into
Saturday morning. Strongly sloped front with strengthening
frontogenetical response resulting in a myriad of precipitation
types and intensity fluctuations. Embedded deep convective cells
only adding to the forecast complexity. Dry air feed from the
north really halting northward progression of precipitation, and
expect this to remain the case, with little if any snow
reaching the northern sections of eastern upper Michigan.
Upstream blossoming area of intense elevated convection across
Wisconsin expected to continue to congeal, riding the elevated
frontal slope into northern lower Michigan overnight into Saturday
morning. Trends continue to support the best activity remaining
along and south of the M-68 corridor. Have growing concern that
training convection within a slowly cooling low and mid level
environment will result in some rather impressive snowfall totals
for interior areas of north central lower Michigan by mid-day
Saturday. Will nudge snow totals up some, but definitely don`t
want to go too extreme based of this highly complex situation.
Cooling from north to south will transition all areas to snow or
a rain/snow mixture by morning, but snow accumulations look to be
far less for areas along and south of M-55.

&&

.NEAR TERM...(Tonight)
Issued at 411 PM EDT Fri Apr 13 2018

...Rain turning to snow tonight...

High Impact Weather Potential...Accumulating snowfall tonight and a
possible light coating of ice.

Primary Forecast Concerns...amounts of snowfall and precipitation
type.

Pattern Synopsis/Forecast...Models are still in consensus on the
track of a developing low pressure system now over the Mississippi
River Valley area and tracking through the southern Great Lakes
region. Deeper moisture ahead of the approaching warm front
associated with aforementioned system is now located just to the
south of our CWA and will continue to produce rain/snow for the next
few hours before changing over to all snow tonight. Accumulations
for northern lower appear to be around 4-6 inches...with higher
amounts north of M-72 to the tip of the mitt, with the higher
terrains receiving the most amounts. Eastern upper Michigan remains
in much drier air with a high pressure system over Ontario ridging
into Lake Superior and will receive only small amounts of
precipitation through the overnight hours. Forecast soundings did
not support freezing rain, as thermal profiles were too cold and
saturated or there were some seeder feeder processes at work. The
only freezing rain in tonight`s forecast will be mainly south of M-
72 as a more pronounced warm nose begins sagging southward to
possibly give a thin glazing on road surfaces and/or trees/
powerlines. Thunderstorms will also be in the forecast through 05Z
as MUCAPE of 300-600 J/Kg along with 3-6km lapse rates near 7.5C
will be enough to fire off some isolated thunder. Any storms that
develop will be elevated in nature. Northeasterly winds will
continue to ramp up throughout the night, reaching 15-20mph with
gusts up to 35mph by morning.

&&

.SHORT TERM...(Saturday through Monday)
Issued at 411 PM EDT Fri Apr 13 2018

...Drawn out messy spring storm system to impact northern Michigan
this weekend...

High Impact Weather Potential: Periods of heavy/wet snow... sleet...
freezing rain...and gusty northeast winds starting later tonight
and continuing into Sunday night.

Pattern Synopsis/Forecast: Large scale split flow pattern across
western North America (a weakish rex block look to things)...with
flow consolidation north of the Great Lakes where southern branch
flow coming around strong troughing over the central/southern
Rockies merges with colder flow coming around an upper vortex over
Hudson Bay.  Southern branch short wave trough will slowly cross the
Plains tonight/Saturday...into the Midwest Sunday...with the
upper low finally reaching the upper Lakes Monday as overall
system takes on a negative tilt.

990mb surface low over far southeast Nebraska at early afternoon
with a strong warm frontal baroclinic zone extending eastward
across southern Iowa/Central Illinois and along the southern
Michigan border. This low is not forecast to move or strengthen
much through the next 24 hours...which makes sense given 3h
pressure rises currently surrounding this system. Low will
eventually move (more like redevelop) eastward along the baroclinc
zone Saturday... tracking into Indiana/Ohio Sunday and as system
goes negative tilt low should slide northward into or east of
Lower Michigan. Surface low never really gets that strong with
this system...the problem lies with the strong surface high over
northern Ontario/Quebec (~1046mb...or 3SD above the mean for mid
April). This will be the impetus for strong east/northeast winds
(and low level cold/dry air advection) across the state this
weekend. Large area of 1+ inch precipitable water values getting
pulled north ahead of the surface low into Missouri/Iowa...so the
stage is set for a messy weekend across northern Michigan. Now to
the details...

Primary Forecast Concerns:  Headline decisions up front...current
Winter Storm Watch for eastern Upper will remain intact. Will add
in the tip of the mitt counties (Charlevoix/Emmet/Cheboygan/Presque
Isle)...that will run from Saturday night through Sunday evening.
These four counties will be put into a Winter Weather Advisory to
cover precipitation tonight. The remainder of northern Lower
Michigan will be upgraded to a Winter Storm Warning from tonight
through the day Sunday.

Precipitation will be ongoing across northern Lower Michigan
Saturday morning...looks like it will be mostly snow though counties
along and south of M-55 may see sleet for a time during the morning.
Decent right entrance region jet dynamics interacting with
isentropic ascent/moisture transport will set the stage for this
precipitation...while a sharp deformation axis and low level
cold/dry air advection looks to keep eastern Upper snow-free into
Saturday evening.  Bulk of the precipitation will be through early-
mid afternoon before tapering off as dry air from the northeast
grabs a stronger foothold.  Snow ratios should be on the low/dense
side (probably at or below 10:1) given deep saturated layer warmer
than -10C (which promotes riming/aggregation).  Also concerned about
how far south the impact of the low level dry air advection on
QPF...as a result will be a bit cautious with snow amounts the
farther north you go (1-2 inches along M-32...2-5 inches south greatest
along/east of I-75 during the day Saturday). Concerned that the
snow may end fairly early across the tip of the mitt counties
Saturday morning...thus the reason not to include these counties
in the warning yet and put them in the watch with eastern Upper
since the bulk of the impact should be Saturday night/Sunday.
Gusty northeast winds (15-25mph with gusts 30+) will blow around
this sloppy snowfall and just make things all around more
miserable.

Round two of this event expected to spread in from the south/southwest
Saturday night...this portion of the event will impact the Upper
Peninsula. This portion of the event also more likely to have
precipitation type problems with a push of low level warm air
(have been trending surface temperatures toward raw model guidance
since a) these work better in cloudy/precip events and b) suspect
statistical (MOS) guidance is having issues with climatology).
The threat for freezing rain/sleet will be increasing across
northern Lower at least up to the M-72 corridor...still
uncertainty with regard to low level thermal fields with
indications in the guidance of gravity waves impacting model
mass/thermal fields (e.g., 850mb thermal ridge into northwest
Lower by 12z Sunday). Ice accumulation is expected to become a
real problem south of M-72 where 0.25 to 0.50+ inch ice
accumulation is possible through Sunday evening. The combination
of snow tonight/tomorrow and freezing rain Sunday is the reason
for a Winter Storm Warning and not an Ice Storm Warning. But if
this ice accumulation comes to fruition combined with continued
gusty northeast winds will result in a significant threat to power
lines.

Meanwhile...looking at mostly snow across eastern Upper though
there are some hints of potential mixed precipitation by Sunday
evening though by then precipitation intensity should wane.
Snowfall amounts across eastern Upper of 8+ inches are anticipated
through Sunday evening.

.LONG TERM...(Monday night through Friday)
Issued at 411 PM EDT Fri Apr 13 2018

High Impact Weather Potential...Minimal.

Still won`t be out of the clutches of our weekend system during the
start of the extended period (Monday night)...though mercifully
short wave ridging finally nudges into Michigan by midweek.  But
another fast-moving (much faster) Pacific-origin short wave trough
will arrive across Michigan by later Wednesday.  This will promise
another round of cyclonic upper level flow (read: not warm) through
the end of the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 734 PM EDT Fri Apr 13 2018

Challenging forecast continues as passing areas of rain and snow,
with embedded enhanced convection briefly changing precip to heavy
snow, continuing across the southern taf locations through
Saturday morning. Still appears KPLN will be just north of the
heaviest snow shield. Lower cigs will be more widespread, once
again south of KPLN. Snowfall will be heaviest across KAPN, with
several inches of wet, heavy snow likely by Saturday morning.
Rain/snow mix will temper accumulations for KTVC and KMBL. Snow is
expected to end later Saturday morning and afternoon, with dry air
also helping scatter out the low overcast. Increasingly gusty
northeast winds overnight and Saturday.


&&

.MARINE...
Issued at 411 PM EDT Fri Apr 13 2018

Gales over Lakes Michigan and Huron continue through Sunday
night...while small craft advisories remain for Whitefish Bay and
the Sault Ste. Marie river. Persistent northeasterly winds tonight
through at least Monday morning...sometimes gusting to 40-45kts.
Winds will begin to diminish Monday morning. Wintry mix of weather
will begin Friday morning and last through at least Monday as well.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING until 5 PM EDT Sunday for MIZ020>036-041-
     042.
     WINTER STORM WATCH from Saturday evening through late Sunday
     night for MIZ008-015>019.
     WINTER WEATHER ADVISORY until 8 AM EDT Saturday for MIZ016>019.
LH...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LHZ345-346.
     GALE WARNING from 2 AM Saturday to 8 PM EDT Sunday for
     LHZ347>349.
LM...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LMZ341.
     GALE WARNING until 8 PM EDT Sunday for LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LSZ321-322.
&&

$$

UPDATE...MB
NEAR TERM...TL
SHORT TERM...JPB
LONG TERM...JPB
AVIATION...MB
MARINE...TL



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