Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 210155 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
855 PM CDT THU OCT 20 2016
Some trepidation about the frost advisory...especially in the
southeast with strato cumulus deck sinking in. However hi-res
model low-level RH forecasts show erosion from the west with cold
and dry air advecting in with surface high...a trend being
supported by current satellite imagery. Surface pressure gradient
is slackening as low pressure continues to move away up the Ohio
River Valley. Expect the light winds and enough breaks in the
cloud cover after 08Z to 09Z for frost to form so no change to
current advisory timing or areal coverage.
Mostly VFR cigs expected overnight, mainly over eastern sections,
though becoming sct to bkn after 08Z. Cigs mainly between 3-4 kft
in most places. There is the potential for some MVFR cigs near or
slightly below 3 kft. Expect clouds to redevelop diurnally and
linger through the day Friday as colder air continues to move in
at the 850 mb level. Winds should remain from the northwest
Friday, with sustained speeds up to 10 kts, especially for the TAF
sites along Lake Michigan.
Allowed northern portion of Small Craft Advisory to expire. Will
have to keep an eye on winds/waves in southern zones to see if
they lower enough for advisory there to expire at 08Z. Waves will
remain in the 2 to 4 foot range through the day Friday with 10 to
15 knot north winds.
.PREV DISCUSSION... /Issued 329 PM CDT THU OCT 20 2016/
Tonight...Forecast confidence medium.
Broad and cool cyclonic flow persists across the Upper Great
Lakes region. Water vapor/RAP loop shows another reinforcing vort
max riding southeast from ern ND/nrn MN. This is proggd to shift
into WI later overnight. Meanwhile the chilly low level thermal
trough is reinforced with the northerly low level windflow. Of
concern is the model proggd LLVL RH progs which shows 70-90
percent for much of the night. However upstream
observations/satellite trends support a scenario more similar to
the consensus of the MOS output where some breaks occur. So given
the chilly 925 temps/current temps/dews do not plan on making any
changes to the going frost advisory.
Friday...Forecast Confidence medium After a frosty start for many
the elongated ridge of high pressure will become centered across
WI setting up a lighter wind regime across srn WI. Low level
thermal trough remains in place with the 500 millibar trough
shifting east of WI during the afternoon. So mid level flow will
take on more of a broad northwest anticyclonic regime. With the
925 temps of 3-4c being dominant it appears reasonable that the
Superblend temps show an extensive amount of low 50s for highs.
Given the lingering mid level cyclonic flow in the morning and the
low level thermal trough would expect cu with the MOS/LLVL RH
progs suggesting this as well.
Friday night through Sunday night...Forecast confidence medium.
A north to south ridge of high pressure will slowly move ewd
across srn WI Fri night into Sat am. Aloft, a weak vorticity
maximum will be passing along with 850-700 mb warm advection. Thus
sct-bkn middle level clouds will be possible late Fri night and
Sat am which will complicate whether a Frost Advisory will be
needed or not. The current forecast for low temps is middle to
upper 30s with some frost expected.
Swly winds and warm advection will develop on Sat and continue
into Sun as low pressure moves from the nrn Great Plains to across
central WI on Sun. 925 mb temps will rise to 10-11C for Sat
afternoon and 11-14c for Sun. High temps will rise once again
above normal with middle to upper 60s on Sun. The cold frontal
passage will then occur late Sun afternoon and continue through
the night. The frontal passage will also be dry with the upper
dynamics remaining to the north and too dry of an airmass in srn
WI for rain.
LONG TERM...Monday through Thursday...Forecast confidence medium.
The cold advection will decrease by Mon am as a large high
pressure area will move across WI through Mon night. A shortwave
trough and low pressure area will then slowly move from the
central Great Plains to across the WI/IL border for Wed night.
There will be good lift and moisture with the low with showers
likely and perhaps a tstorm for Wed and Wed night. Rain chances
however will begin on Tue. Thu looks to be dry for now but with
cloudy conditions in the low`s wake. High temps will be near
normal with warmer than normal low temps due to the clouds.
AVIATION/00Z TAFS/...Large surface high approaching from the
Plains with the cool northerly flow persisting between an Ohio
Valley low and associated frontal boundary and the Plains high.
Broad cyclonic flow persists with another shortwave sliding
southeast from ND. Increasing amplitude to the low level thermal
trough with 850 temps dropping to -2 to -5c by morning. 850 and 925
rh progs suggest MVFR cloud deck may be stubborn overnight but
seeing quite a bit of breaks upstream in northern WI with quite a
bit of cellular/diurnal appearance taking shape. Low level thermal
trough persists into Friday though mid level cyclonic flow eases a
bit Friday afternoon.
MARINE...A Small Craft Advisory remains in effect due to the north
winds and subsequent higher wave action with the favorable fetch. Am
expecting the winds to gradually subside as low pulls further away
and high pressure ridge draws closer. Will not modify end time yet
however if gradient does not relax as quick the higher waves could
then linger longer necessitating an extension.
WI...FROST ADVISORY from 1 AM to 8 AM CDT Friday for WIZ046-047-051-
LM...SMALL CRAFT ADVISORY until 3 AM CDT Friday for LMZ645-646.
TONIGHT/Friday AND AVIATION/MARINE...Collar
Friday NIGHT THROUGH Thursday...Gehring