Area Forecast Discussion
Issued by NWS Goodland, KS

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657
FXUS63 KGLD 141204 CCA
AFDGLD

Area Forecast Discussion...CORRECTED
National Weather Service Goodland KS
504 AM MST Sat Jan 14 2017

.SHORT TERM...(Today and tonight)
Issued at 502 AM MST Sat Jan 14 2017

Our forecast area is still on track for winter storm, however
changes were made to ongoing forecast to reflect latest trends.

GFS/GEFS remain outliers in evolution of upper level pattern and
ECMWF/NAM and other guidance were favored for timing, blends, and
adjustments.

A dry air mass is in place over our CWA roughly below 800mb. Mid to
high level moisture is increasing across the region, but forcing
remains weak. This dry layer will be prohibitive to measurable
precipitation through at least 00Z and there are some indications
in short range and high resolution guidance that this will not be
overcome until late tonight for the majority of our CWA. In fact
consensus of short range guidance would not support measurable
precipitation until after midnight for our entire CWA and then on
the far southeast until 12Z Sunday. ECMWF still supports potential
light freezing rain as early as 00Z, but confidence is diminished
in impacts for the majority of our CWA until later.

A colder near surface layer advertised by the NAM and implied by
much colder Tw from ECMWF/ARW/NMM may support more in the way of
sleet accumulations one may areas of moderate precipitation begin to
slide across our CWA. This would obviously decrease freezing rain
accumulations and shift impacts from being primarily focused on
power outages to just travel. In any case travel will be very
difficult once this event gets underway with worst conditions Sunday
through Monday.

ECMWF/NAM both show the closed low tracking Sunday night and Monday
in such a way as to support a deformation band forming in our
central or western CWA and a complete change over to snow Monday.
Based on conservative QPF/snow ratios we could see 8" or higher.
This may be dependent on the slower upper low track of ECMWF/NAM and
slightly better snow ratios. I trended snow totals upwards as
previous blends were being influenced downward by the GFS which
likely is not handling this track very well and is a large outlier.
SREF mean is near the current forecast, however the SREF plume shows
how large the spread between various members with minimal
clustering. Heaviest band may not impact as large of an area and
there is still the possibility that sleet could diminish totals.
This large ensemble spread is reflecting this uncertainty.

Regarding highlights: As a result in the drier early trend I delayed
the onset of the Ice Storm Warning until 00Z and the Winter Storm
Watch until 09Z. I am still confident in measurable (potentially
high impact) ice accumulations where the Ice Storm Warning is in
place, though if sleet dominates our amounts may need to be trimmed.
Regarding the Watch: Confidence in freezing rain or sleet/snow
amounts are still somewhat low due to potential for more sleet
Sunday and spread in snow totals Sunday night and Monday. Due to the
delay in onset and complications of impacts I felt it was best to
hold off on upgrading the watch.

.LONG TERM...(Tuesday through Friday)
Issued at 159 AM MST Sat Jan 14 2017

Forecast concerns will be affects of upcoming storm on temperatures
at the beginning this period, and the next chance of precipitation
toward the end of the period. Satellite showing a progressive flow
over most of the Pacific with an amplified/split flow over the
western portion of the North America.

Temperatures at the beginning of this period look to be problematic
depending on the extent/amount of ice/snow this upcoming storm will
drop on the area. There definitely looks like there will be a lot of
ice around over the current ice storm warning area. There is still
some uncertainty on how much snow and where it will fall. All in all
the entire forecast area looks to be covered with a decent amount of
snow and/or ice. So the first couple of days I reduced the the maxes
a few degrees. This will have to be looked at and adjusted again.

Through this entire period there is a big spread in both the
deterministic and ensemble output. This is all because the models
are having a hard time resolving what happens with the incoming
trough after it moves to our east. This also has affects on how the
models handle the end of the week trough. The deterministic output
at times toward the end of the period is out of phase with each
other. Currently the forecast builder gave me pops Friday and couple
of periods beyond. Depending on the deterministic output and the
ensemble output, they would indicate the possibility of
precipitation occurring 24 to 48 hours before that.

Because of this uncertainty and disagreement, left alone the pops
the forecast builder gave me. Hopefully the output can start getting
into better agreement.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 502 AM MST Sat Jan 14 2017

VFR conditions are expected to prevail at both KGLD and KMCK
terminals through at least the early evening. Winds will remain
light and variable. Models have trended slower on onset of
freezing precipitation and this delay was reflected in this TAF
update with FZRA and MVFR cigs delayed until 09z. I still can`t
rule out a few pockets of rain or freezing rain before this period
but confidence is very low in coverage and decision was made to
limit mention. Freezing precipitation is not currently expected at
KMCK during this TAF period, though conditions will be
deteriorating after this TAF period.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Winter Storm Watch from late tonight through Monday afternoon
     for KSZ001>003-013-014-027.

     Ice Storm Warning from 5 PM MST /6 PM CST/ this afternoon to 11
     AM MST /noon CST/ Monday for KSZ004-015-016-028-029-041-042.

CO...Winter Storm Watch from late tonight through Monday afternoon
     for COZ090>092.

NE...Winter Storm Watch from late tonight through Monday afternoon
     for NEZ079>081.

&&

$$

SHORT TERM...DR
LONG TERM...BULLER
AVIATION...DR



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