Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 241740

Area Forecast Discussion
National Weather Service Gaylord MI
140 PM EDT SUN JUL 24 2016

Issued at 1027 AM EDT Sun Jul 24 2016

...Marginal risk for severe thunderstorms continues...

Per the northern Michigan usual, one complicated and low confidence
convective forecast this afternoon into this evening. Morning MCS
continues to run its course to our south, riding instability
gradient across southern lower Michigan. Area of decaying stratiform
rain on its northern periphery, clipping areas down near Saginaw
Bay. Band of MCV/low level jet driven showers further north has now
exited into northern Lake Huron and Ontario. Thus, most of the area
at this hour is devoid of any precipitation, with even some pockets
of clearing in post-MCS/MCV subsidence regime. Actual cold front
remains well upstream per surface observations, cutting across
western Wisconsin. Pre-frontal deep moist advection continues, with
surface dewpoints pushing through the upper 60s/lower 70s and pwat
values nearing 2 inches (12z local and KGRB soundings had pwat
values of 1.89 inches and 2.02 inches respectively).

What occurs hereafter is still riddled with uncertainty. Simple
extrapolation suggests cold frontal passage will not occur until
this evening, leaving plenty of time for further destabilization.
Breaks in the overcast will only help the cause, with some of the
latest HRRR/NAM-12 progs supporting upwards of 3000 j/kg of surface
based cape by this evening. Deep layer forcing remains lacking,
leaving actual surface based convergence ahead of approaching front
(even some hints of pre-frontal pockets of convergence through
overland heating) to drive convection. Do believe thunderstorms will
likely form later this afternoon into early evening, although per
lack of deep forcing (virtually no mid level height falls until well
after frontal passage) expect coverage to remain fairly scattered.
Isolated severe weather remains possible, especially if some of the
higher cape values are realized, with 35 to 45 knots of effective
shear and hints of good cape through the favored hail growth zone.


.SHORT TERM...(Today and tonight)
Issued at 338 AM EDT Sun Jul 24 2016

High impact weather potential: severe storms possible late today.

A typically messy forecast dealing with deep convection. Deep warm
advection is in place, ahead of a cold front moving into central MN
and nw Iowa. Warm advection is a little stronger to our west than
here. Initially, main areas of active deep convection were well to
our south (northern IN/far sw lower MI) and well to our west
(central MN). However, a shortwave moving into ne WI is contributing
to some showers/t-storms there on up into the central UP. Thunder
is concentrated between GRB and MKE, along an instability gradient
that is moving into the region. Convective trends up through cold
frontal passage are the main concern.

Today/this evening...sct/nmrs showers/t-storms will cross the region
this morning, especially early. Activity will diminish and/or push
off to the east toward late morning, as shortwave moves downstream
with subsidence in its wake, and as the low level jet (briefly)
decreases somewhat. Most recent HRRR runs have very little precip
after 15z/16z. Do not anticipate this activity posing a svr
threat, running into a less stable airmass over northern MI
(mucapes in mid-triple digits).

Cold front will move east across the forecast area between 00z and
06z. Height falls will be meager/non-existent until the front
arrives. That likely results in a lull period after morning precip
diminishes and before the front arrives, thanks to capping aloft
(700mb temps 9-10c). Morning activity/associated cloud cover should
thin out early enough to allow for reasonably healthy
destabilization, especially in nw lower MI. Mlcapes of around
1500j/kg should emerge by early evening (more than that just
upstream in eastern WI). However, some of that instability may
diminish in spots by the time the front/marginal cooling aloft

Per most model progs, doubt that upscale growth will be fast enough
to produce widespread convection with fropa. Will return sct pops in
western sections just before 00z, then have them across the entire
forecast area this evening. Do believe there is a reasonable
potential for some svr storms, given instability and shear (0-6km
bulk shear 30-35kt) present. Some potential for supercells early on
(centered on 00z), when considerable directional shear is present.
Hodographs straighten out as the front arrives, suggesting an
evolution to a wind threat.

Degree of severe threat is dependent on how quickly we can clear out
(presuming we do). If nw lower MI starts to see some sunshine by
noon, we/re probably in for a busy day. Not quite so much if it
waits until 3pm or so. Window for potential svr looks to be
between 4 pm and midnight.

Max temps 80s, and quite humid (dew points upper 60s to lower 70s).

Overnight...some spotty post-frontal showers could linger a bit past
06z, but anticipate that will exit by 12z as dry slot pushes into
the region. Low clouds will linger thru morning in most areas. Cold
advection will be less than impressive, keeping min temps in the
lower 60s to around 70f.

.LONG TERM...(Monday through Saturday)
Issued at 338 AM EDT Sun Jul 24 2016

Pattern/Expected Evolution: An area of low pressure and accompanying
upper level wave will continue to move east as heights increase and
surface high pressure builds over the Great Lakes region.

Models are in fairly good agreement with lingering clouds Monday
morning over northeast lower and especially eastern upper as said
low pressure departs east and accompanying shortwave lags just a
bit. Heights will then build throughout the day Monday afternoon as
the upper level ridge and surface high pressure builds over the
Great Lakes region. This high pressure will dominate northern
Michigan`s weather through Tuesday at least, with precipitation-free
weather, daytime temperatures in the upper 70s to mid 80s and lows
in the upper 50s to low 60s. Broad troughing begins taking over the
Great Lakes region Wednesday as the ridge amplifies over the
northwest CONUS/western Canada, increasing cloudiness and chances of
precipitation. A shortwave traversing this broad area of troughing
with attendant moisture may be enough to fire off some showers and
possibly even some thunder. Wednesday`s highs will continue to reach
into the 80s.

Extended: (Thursday through Saturday)

Troughing will remain over the region, with several shortwaves and
ample moisture to develop periods of rain and thunder throughout
much of the period. Although pops are in every day of the extended
forecast, by no means will it be a washout. There will be partly to
mostly cloudy skies with periods of rain/thunder here and there
throughout the period. High pressure begins to finally build back
into the region towards the very tail end of the extended forecast,
decreasing precipitation chances. Daytime temperatures will cool
slightly, reaching only into the mid 70s to low 80s, while lows will
remain in the upper 50s to near 60.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 137 PM EDT Sun Jul 24 2016

Plethora of cig heights out there this afternoon, ranging from
mostly clear skies to mvfr causing stcu. This trend should
continue through the remainder of the afternoon. Confidence is
very low with regards to additional shower and thunderstorm
development later today into the evening as a cold front crosses
the taf sites. Will cover with vicinity wording for now. Of
course, any storms that do impact taf locations will temporarily
result in gust winds and lower cigs/vis. Band of mvfr clouds to
briefly follow this front tonight, with trends supporting rather
aggressive clearing towards morning. Mostly sunny and a touch
breezy heading through Monday morning.


Issued at 338 AM EDT Sun Jul 24 2016

Somewhat breezy sw winds will be seen today, just in advance of a
cold front that crosses northern MI this evening. Small craft
advisories already up for the nw lower MI coast and Whitefish
Bay, will be assessing potential elsewhere (in particular down by
OSC/Tawas) shortly. Breezy nw winds arrive very late tonight into
Monday behind the cold front. Showers and t-storms (some of which
could be strong) will be a threat until the cold front passes.


.APX Watches/Warnings/Advisories...
LM...SMALL CRAFT ADVISORY until 6 PM EDT this evening for LMZ342-

LS...SMALL CRAFT ADVISORY until 6 PM EDT this evening for LSZ321.



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