Latest ZFP from WFO RIW

		
National Weather Service Local Forecast for Star Valley Ranch
Updated: 21 May 05:16 am MDT

Overnight... A 20 percent chance of snow showers.  Mostly
cloudy, with a low around 33. Calm wind. 

Tuesday... Rain and snow showers likely before 8am, then rain
showers. Some thunder is also possible.  High near 49. Calm wind
becoming west northwest 5 to 7 mph in the afternoon.  Chance of
precipitation is 80%. Little or no snow accumulation expected. 

Tuesday Night... Showers and possibly a thunderstorm.  Low
around 35. West northwest wind around 5 mph becoming calm  in the
evening.  Chance of precipitation is 80%. New precipitation amounts
between a quarter and half of an inch possible. 

Wednesday... A chance of rain and snow showers before 8am, then
a chance of rain showers. Some thunder is also possible.  Cloudy, with
a high near 47. North northeast wind 3 to 7 mph.  Chance of
precipitation is 50%. Little or no snow accumulation expected. 

Wednesday Night... A chance of rain showers before 11pm, then a
chance of rain and snow showers between 11pm and 4am, then a slight
chance of snow showers after 4am. Some thunder is also possible. 
Mostly cloudy, with a low around 32. East wind around 7 mph.  Chance
of precipitation is 30%.

Thursday... A chance of snow showers before 7am, then a chance
of rain and snow showers between 7am and 9am, then rain showers likely
after 9am. Some thunder is also possible.  Mostly cloudy, with a high
near 47. East northeast wind 5 to 8 mph becoming south southeast in
the afternoon.  Chance of precipitation is 60%.

Thursday Night... A chance of showers and thunderstorms. 
Cloudy, with a low around 35. South southwest wind 3 to 6 mph.  Chance
of precipitation is 50%.

Friday... A chance of showers, with thunderstorms also possible
after 1pm.  Cloudy, with a high near 51. Chance of precipitation is
30%.

Friday Night... A 20 percent chance of showers and
thunderstorms before midnight.  Mostly cloudy, with a low around 35.

Saturday... A 30 percent chance of showers and thunderstorms
after noon.  Partly sunny, with a high near 59.

Saturday Night... A chance of showers and thunderstorms. 
Mostly cloudy, with a low around 35.

Sunday... A slight chance of showers and thunderstorms.  Partly
sunny, with a high near 63.

Sunday Night... A slight chance of showers and thunderstorms. 
Mostly cloudy, with a low around 37.

Memorial Day... A chance of showers and thunderstorms.  Mostly
cloudy, with a high near 59.

		

Latest AFD from WFO RIW

		National Weather Service Riverton WY
243 AM MDT Tue May 21 2019

.SHORT TERM...(Today through Thursday night)

The main 500mb low is currently spinning over the Four Corners
Region at the moment. A stationary sfc boundary remains along the
Divide of Wyoming. Southwest of the sfc boundary, an occasional
flare up of convection with isolated lightning has been taking
place, with just left over showers on the other side of the
boundary. The main 500mb low will redevelop as cyclogenesis takes
place over Southeast Colorado by 12Z this morning. This will set
us up for another round of a cold stratiform precipitation event,
mainly east of the Divide. The heaviest precipitation will take
place across Natrona and Johnson Counties today and tonight where
the heaviest wrap around precip will occur as the low tracks north
along the Plains states. Although the heaviest purely “wrap
around” precip will likely take place in Johnson County, the
upslope that occurs around the Casper/Casper Mountain area will
balance out the amounts. The NAM indicates -9.5C temps wrapping
around into Johnson County and -8C over Natrona County. With the
amplified QPF of a half to three quarters and sufficiently cold
temperatures at 700mb, we will include the lower elevations of
Natrona and Johnson Counties for a late May Winter Weather
Advisory along with the East Slopes of the Wind River and Big Horn
Mtns as well as Casper Mountain. However, we will not start the
low elevation advisories until 00Z Wednesday. All the advisories
will end at 18Z Wednesday. The mountains will actually witness
warning amounts, but with the minimal impact and strong May sun
interacting with the snowfall this afternoon, will keep these
mountain zones in an advisory, which, by the way, began at 06Z
this morning. The mountain advisories will also go through 18Z
Wednesday. The only missing element will be the wrap around
isentropic lift that the earlier model runs were indicating. The
least amount of precip from this event will occur west of the
Divide over Northwest Wyoming, farthest away from the low, and
where downslope flow will occur. Snow levels west of the divide
should run about 6K.

After 18Z Wednesday, the back edge of the precip will gradually push
off to the north to our northern zones. The least amount of precip
anywhere across the CWA will likely take place between 00Z and 06Z
this evening as  one batch of precip exits to the north and the next
large area of precip moves in from the south. This next area of
precip will be associated with the kicker that is now approaching
the Pacific Northwest and is progged to be located over the Great
Basin by Thursday, as both this low and the exiting low “dumbbell”
around each other.  This large glob of precip will rapidly shift
north, mainly across the east half of the CWA Thursday, given the
strong southerly difluent flow once again ahead of the low, which
will track to Northwest and Northern Wyoming by the models by
Thursday night, along with the associated strong QG forcing. The
precip will taper off in intensity during the night Thursday night.
Snow levels with this weather system should run about 6k east of the
Divide and 7500 feet west.

Any thunderstorms that occur through Thursday will be relegated to a
few isolated afternoon storms west of the Divide through Thursday.

.LONG TERM...(Friday through Tuesday)

The first part of the forecast should feature a general decrease in
activity across the area. The upper level low that brings the
precipitation for Thursday will have lifted north of the state by
that time. Enough wrap around moisture may be present for a few
showers and thunderstorms, mainly of the afternoon variety, on
Friday but these would be confined to the west and northern
portions of the area and even here most of the day should turn out
to be largely rain free. We may even see some glimpses of that
round orb in the sky. What is that thing called? Oh yeah, the sun.
Temperatures will turn much milder as well, but still be below
normal.

Transitory ridging will build over the state for Saturday. At this
point, this looks to be the least active of the extended period.
For the most part, we kept POPs in the chance of less range with
areas East of the Divide largely dry. The GFS is wetter but tends
to have a wet bias this far out as well as a fast bias so we went
closer to the European guidance.

As the ridge shifts to the east of the area and an upper level low
tries to approach from the south and west, convection will again
become a little more numerous although it should remain largely
diurnal on Sunday and Monday with a good portion of each day rain
free. Temperatures will continue to slowly moderate but will
remain near to somewhat below normal for most locations. Tuesday
at this point may turn out to be the most active day but still a
lot of uncertainty, as there usually is this far out.
&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)

Cloud decks will continue to lower into primarily MVFR, local IFR
categories vicinity and southeast of a KBPI-KSHR line early this
morning as the next round of RA/SN moves in from the southeast.
Most areas will start as a mix before transitioning to all snow
early this morning. Most areas will remain light, but some heavier
SHSN may briefly lower vis.

Only areas that will keep some form of rain would be COD and WRL.
After sunrise, temperatures will rise enough to switch all
aerodromes to rain, which is expected to continue through the
remainder of the afternoon. The precipitation chances remain in
the forecast Tuesday evening, but some slight increases in cigs are
possible. Precipitation may again transition back to snow by
midnight Tuesday night, with sporadic vis lowering..

&&

.FIRE WEATHER...

Cool and wet weather will persist through Thursday with the most
precipitation and coldest weather to occur east of the Divide.
Significant snowfall will occur in zones 280, 281, 285, 288, and
300, east of the Divide through Wednesday morning. An isolated
thunderstorm is possible west of the Divide through Thursday.
Smoke dispersal this afternoon will range from fair to good.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Wednesday for WYZ009-015-
022.

Winter Weather Advisory from 6 PM this evening to noon MDT
Wednesday for WYZ010-011-020.

&&
		

Latest GFS MOS for JAC

		KJAC   GFS MOS GUIDANCE    5/21/2019  0600 UTC
DT /MAY  21      /MAY  22                /MAY  23             /
HR   12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 00 06
X/N              48          34          49          33       50
TMP  34 39 44 45 43 40 36 36 35 40 45 46 46 42 39 37 34 43 48 47 38
DPT  32 34 33 34 36 38 36 36 35 35 31 30 29 30 31 30 31 31 27 32 37
CLD  OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV
WDR  36 34 26 27 01 35 36 01 01 35 35 36 36 01 36 01 01 35 35 01 05
WSP  02 03 06 06 08 08 06 08 11 11 10 17 22 14 17 13 23 19 15 08 04
P06        32    71    61    34    41    45    25    16    15 39 51
P12              90          75          62          31       47
Q06         1     2     1     1     1     1     0     0     0  1  1
Q12               2           2           1           0        1
T06      4/ 0 51/ 0 19/ 0  1/ 0  2/ 0 27/ 0  5/ 0  1/ 0  0/ 0 13/ 0
T12                 58/ 0        3/ 0       29/ 0        1/ 0 27/ 0
POZ   1  0  0  0  0  0  0  0  1  0  0  0  0  0  0  0  1  1  0  0  0
POS  61 61 44 32 22 32 47 58 56 44 37 35 36 45 52 53 44 47 39 23 38
TYP   S  S  R  R  R  R  S  S  S  S  R  R  R  R  S  S  R  S  R  R  R
SNW                           0                       0
CIG   6  6  6  6  6  6  6  6  6  6  6  6  6  7  7  7  7  7  7  6  6
VIS   7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7  7
OBV   N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N  N




904
FOUS26 KWNO 210600

-----------------

KJAC   GFSX MOS GUIDANCE   5/21/2019  0000 UTC
FHR  24| 36  48| 60  72| 84  96|108 120|132 144|156 168|180 192
TUE  21| WED 22| THU 23| FRI 24| SAT 25| SUN 26| MON 27| TUE 28 CLIMO
X/N  50| 34  48| 31  51| 33  50| 35  57| 36  56| 37  60| 34  61 34 65
TMP  45| 36  46| 32  48| 35  47| 37  53| 37  51| 39  56| 35  58
DPT  36| 36  28| 29  33| 35  36| 37  35| 37  40| 36  38| 34  37
CLD  OV| OV  OV| OV  OV| OV  OV| OV  OV| OV  OV| OV  OV| OV  OV
WND   8| 12  21| 27  27|  9   8|  8   7| 12  12| 15   7| 10  12
P12  83| 67  62| 28  52| 74  70| 43  51| 31  33| 38  38| 37  30999999
P24    |     87|     61|     83|     73|     49|     60|     49   999
Q12   2|  2   1|  0   1|  2   3|  2   3|  1   2|  4    |
Q24    |      2|      1|      3|      2|      1|       |
T12  55| 20  26|  7  16| 15  40| 20  40| 22  24| 26  32| 21  21
T24    | 68    | 26    | 26    | 53    | 45    | 44    | 44
PZP   1|  1   2|  0   2|  1   0|  1   2|  0   0|  0   1|  0   0
PSN  27| 24  23| 42  31| 28  15|  8   7| 12  13| 14   9| 10  11
PRS  24| 29  20| 10  19| 17  25| 26  19| 18  18|  7  11|  8   9
TYP  RS| RS  RS| RS  RS| RS   R|  R   R|  R   R|  R   R|  R   R
SNW    |      0|      0|      0|      0|      0|       |