Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/16/17
Area Forecast Discussion
National Weather Service Grand Rapids MI
929 PM EST Fri Dec 15 2017
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 322 PM EST Fri Dec 15 2017
The lake effect snow showers that impacted the area this morning are
diminishing this afternoon. This will continue into early this
evening. Another band of light snow will develop this evening south
of I-96, and will migrate north through Saturday morning before
ending. 1 to 3 inches of new snow will be likely.
A lull in the snow is expected then Saturday night and early Sunday.
Precipitation chances will increase once again later Sunday. The
precipitation will start as some rain or snow as warmer air moves
in, and continue through Monday night before ending.
&&
.UPDATE...
Issued at 929 PM EST Fri Dec 15 2017
I have issued a Winter Weather Advisory overnight till 10 am
Saturday morning for 2 to 4 inches of snow. Nearly all of the Hi-
Resolution models for several runs in a row now are forecasting
around 0.30 inches of QPF from this warm advection/isentropic lift
event overnight. The 18z and 00z NAM and several runs of the HRRR
and RAP model show around 50 knots nearly perpendicular to the
anisotropic surfaces tonight (around midnight). The focus of the
heaviest precipitation is from Southeast Kent County northwest
across Ottawa into Southern Muskegon County. Since warm advection
events tend to over preform I though it best to issue the Winter
Weather Advisory for the counties with the heaviest snowfall
overnight.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 322 PM EST Fri Dec 15 2017
Our main focus of the short term is now the light snow expected
tonight, and then p-type questions for Sunday and Sunday night. The
advisory for today will be allowed to expire on time with the new
forecast package.
Lake effect snow showers are on the declining trend this afternoon
with regards to intensity and coverage as expected. The short wave
that helped the uptick today, is now moving east of the area. This
is driving down the inversion heights for a bit.
The break in snow will be short lived, especially for the Srn
portion of the CWFA. We will see a sfc trough/cold front over the
central portion of the area, drive south to I-94 this evening before
stalling. It stalls out as upper heights start to build also this
evening. We will see a wave of moisture transport translate along
the front and develop a band of light snow.
This looks to develop a NW to SE band of light snow later this
evening, that will gradually shift north to be centered around I-96
by Sat morning. This does not look to be significant enough to
warrant another advisory, but will drop 1-3 inches over a 12-18 hour
time frame. It will end as the wave moves east of the area Sat
afternoon.
The next situation will be incoming pcpn late Sun and Sun night. We
will see a short wave across the Central and Southern Plains lift NE
into the area. This wave will be different from the series of waves
we have seen over the past couple of weeks since it will be coming
from the SW. This will allow warmer air to push up into the area.
The pcpn may start out as some snow initially. It will tend to
change over with a SW low level flow advecting above freezing air,
and a sufficient melting layer depth to likely change it over to
rain for at least srn areas Sun night as temps warm.
It does not look like this system will produce significant impacts.
We will monitor it in case temps do not warm quick enough, and p-
type becomes a problem.
.LONG TERM...(Monday through Friday)
Issued at 322 PM EST Fri Dec 15 2017
Active pattern continues in the extended with two lows moving
through separated by a period of lake effect snow.
The first storm early in the week does not look to have much impact
as the southern stream moisture remains well separated from the
dominant northern stream and the sfc low passes well north of the
forecast area. Cold front comes through Monday night with cold
advection and lake effect snow showers Tuesday and Tuesday night
then tapering off Wednesday as warm advection begins ahead of the
next low. Bumped up Superblend POPs for lake effect snow showers
during this time period.
The second low comes through Thursday into Friday and continues to
have a lot of ensemble spread between a further north, stronger low
and a weaker, more southern track that would be colder with mostly
snow instead of mostly rain. The 12Z operational GFS and ECMWF have
flip flopped with each other since yesterday with the ECMWF now
having the less amplified, colder solution. Did not make any changes
to the POPs or temperatures during this time as the blend still
looks like a good compromise.
Looking beyond Friday and to December 25th...the overall synoptic
pattern shows a polar vortex across Eastern Canada and a SE CONUS
upper ridge. There is a very impressive temperature gradient between
the Great Lakes and Central Atlantic coast, with arctic air and 850
mb temperatures of -20C in Lower Michigan and a balmy plus 12C near
Cape Hatteras.
We will have to closely watch where the southern edge of the arctic
air and tropical moisture feeding up from the Gulf meet. At this
point it appears we will be solidly in the cold air with some lake
effect snow showers while there could be a band of heavy freezing
rain somewhere to our south...potentially across the Ohio Valley.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 618 PM EST Fri Dec 15 2017
As the current round of lake enhanced snow showers come to an end,
a band of warm advection snow will spread northward though the TAF
sites overnight. The I-94 TAF sites will have only light snow, and
that will mostly be prior to 08z. With the heaviest snow being in
the 03z to 06z time frame. Meanwhile for I-96 TAF sites the band
snow will last longer and have heavier snow assoicated with it.
It should be solid IFR for MKG, GRR and LAN for at least 6 hours
(06z through 12Z).
After the snow ends, the I-94 TAF sites may see the low clouds
break up and ceilings be VFR, on the other hand, for the I-96 TAF
sites I could see solid IFR cigs maybe even some fog. This could
be problem if surface temperatures stay below freezing (more than
likely will).
&&
.MARINE...
Issued at 322 PM EST Fri Dec 15 2017
We will be allowing the current Small Craft Advisory to go on as is
for now. Most of the current obs along the shore continue to support
advisory conditions. Winds will gradually ease up, and waves will
slowly follow suit. The 5 am expiration time looks good at this
point.
&&
.HYDROLOGY...
Issued at 322 PM EST Fri Dec 15 2017
Many rivers have iced over due to the snow and cold temperatures.
The Looking Glass near Eagle has risen above bankfull due to
downstream ice constricting the flow. It is expected to gradually
fall but some fluctuations are still possible. High temperatures
above freezing early next week will soften the ice a bit. Water
frozen in the snowpack ranges from 0.5 to 1 inch in most locations,
but a full snowmelt is not expected anytime soon.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EST Saturday for MIZ050-051-
056>059-064>067.
LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849.
&&
$$
UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Ostuno
AVIATION...WDM
HYDROLOGY...CAS
MARINE...NJJ
Area Forecast Discussion
National Weather Service Lincoln IL
806 PM CST Fri Dec 15 2017
.UPDATE...
Issued at 805 PM CST Fri Dec 15 2017
Earlier batch of altocumulus is exiting the northeast fringes of
the forecast area this evening. More expansive area of mid and
high clouds, currently to our northwest, has begun to spill into
central Illinois. Latest humidity progs off the RAP model suggests
this overspreading areas along and north of I-72 past midnight,
but shifting eastward with time and moving out before sunrise.
With southwest winds averaging around 10 mph overnight, not a lot
of additional temperature dropoff is expected. Going forecast had
a good handle on this, and only needed some minor adjustments to
reflect latest trends.
&&
.SHORT TERM...(This evening through Saturday)
ISSUED AT 255 PM CST Fri Dec 15 2017
A weak disturbance will bringing another batch of stratocumulus
clouds (ceilings 4-6k ft) se into central IL and along and
Champaign to Taylorville line at 230 pm. An area of light snow and
flurries was over ne IL and skirting far ne CWA along and ne of a
Henry to Chenoa to Hoopeston line. 1002 mb surface low pressure
was over eastern upper MI and will track to along the southern
Quebec and Ontario province line this evening, taking its light
snow/flurries out of area late today. Low clouds will decrease
early this evening though mid level clouds to continue into
this evening and decrease during overnight. Clouds along with sw
winds 8-13 mph to keep temps from falling too much tonight, with
lows in the upper 20s to around 30F.
A nice day ahead on Saturday with a fair amount of sunshine and sw
winds 10-15 mph and gusts to 20 mph bringing milder temperatures.
Highs range from the upper 40s to around 50F along and ne of I-74
to the mid 50s from Springfield sw.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 255 PM CST Fri Dec 15 2017
Dry weather continues Saturday night as clouds increase by overnight
ahead of wx system taking shape in the southwest states. Lows in the
low to mid 30s, coolest along and ne of I-74. Weak surface low
pressure to eject ne from the southern plains and into nw IL
Sunday afternoon. Precipitation to spread quickly ne across
central IL during Sunday morning and could start as a mix along
and north of I-74 early Sunday morning before becoming all rain.
This system is a quick mover and precipitation already
diminishing from the sw later Sunday afternoon, with rainfall
amounts only up to a tenth inch possible. Highs Sunday in the mid
to upper 40s but these readings still a good 10 degrees above
normal for mid December. A weaker disturbance ejects ne and
brings small chances of light rain showers overnight Sunday night
into Monday morning. Lows Sunday night in the mid to upper 30s.
Highs Monday in the upper 40s north of Peoria and mid 50s by
Lawrenceville.
A dry stretch of weather expected from Monday afternoon through
Thu morning across CWA as storm tracks will be across the Great
Lakes and over the southeast states by a frontal boundary. Above
normal temps continue with highs 45-55 Tue thru Thu. Latest ECMWF
model now showing surface low pressure tracking into the mid MS
river valley by Wed afternoon and brings qpf into southern half of
IL Wed and Wed evening. This will need to be watched but for now
we stayed with consensus of a dry forecast during that time which
GFS and GEM show. A deepening upper level trof over the Rockies by
Thu to eject a weather system into the upper Midwest late Thu and
deepen surface low pressure ne into the southeast Great Lakes Fri
afternoon. Continued small chances of rain showers over IL river
valley late THu afternoon, then spread chances of precipitation
se across CWA during Thu night with rain turning to snow showers as
colder air usher in. Temps cool back closer to normal for next
Friday. 12Z GFS and ECMWF models show an active southern stream
storm track during Christmas weekend and will need to be watched
for holiday travelers. Latest models currently keep precipitation
south of CWA next weekend, but models have not been consistent
from previous runs and also GEM model not in best agreement with
GFS and Ecmwf.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 520 PM CST Fri Dec 15 2017
Cloud deck around 6,000 feet is pulling eastward and should be out
of the TAF sites in the next few hours. Larger area of mid and
high clouds is streaming southeast and will shift eastward over
central Illinois overnight, but will not pose an aviation impact.
Southwest winds should average around 10 knots throughout the
period.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Geelhart
SHORT TERM...07
LONG TERM...07
AVIATION...Geelhart