Alert archive / Oregon / Mesoscale Discussions in 2021
Mesoscale Discussion 71
The Storm Prediction Center issued this mesoscale discussion at Feb 12, 2021, 5:55 PM PST for Polk County, Washington County, Yamhill County, Oregon. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- Feb 12, 2021, 5:55 PM PST (01:55 UTC)
- Expired
- Feb 12, 2021, 11:00 PM PST
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Freezing rain
Counties Polk County, OR, Washington County, OR, Yamhill County, OR
The radar
The Portland,OR radar (KRTX), 56 km from the middle of the area, began a volume at 01:56 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The nearest sounding before it
Salem/Mcnary, OR (KSLE), launched 00:00Z, 1.9 hours before the alert went out and 42 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 9 J/kg
- Mixed-layer CIN
- 0 J/kg
- Mixed-layer LCL
- 389 m above ground
- 0-6 km bulk shear
- 44 kt
- 0-1 km storm-relative helicity
- 342 m²/s²
- 0-3 km storm-relative helicity
- 427 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
620
ACUS11 KWNS 130155
SWOMCD
SPC MCD 130155
ORZ000-130700-
Mesoscale Discussion 0071
NWS Storm Prediction Center Norman OK
0755 PM CST Fri Feb 12 2021
Areas affected...Portions of Willamette Valley
Concerning...Freezing rain
Valid 130155Z - 130700Z
SUMMARY...Freezing rain rates are expected to increase this evening,
especially within the 7-11 PM time window. Areas within the
Willamette Valley west of Portland are most likely to see higher ice
accumulations. Precipitation in Portland will remain snow with a
transition to freezing rain and sleet towards early Saturday
morning.
DISCUSSION...Surface high pressure into the Columbia Basin has
helped to maintain easterly/northeasterly surface winds into the
Willamette Valley. With the approach of a strong Pacific trough this
evening, coverage and intensity of precipitation should increase.
Current KRTX reflectivity trends indicate that this process is
underway. Light freezing rain has been observed for several hours
from just west of Portland and southward to near Salem. These areas
are the most likely to see larger ice accumulations. While Portland
is currently observing snowfall, it will be near the transition zone
to freezing rain/sleet. Forecast soundings do indicate that freezing
rain and sleet are possible towards 2-4 AM PST. The exact evolution
of the transition zone will be dependent on the surface low
developing west of the Washington coast. Current observations
indicate a preference for a more northerly track which would
indicate higher probability of transition away from snow later
tonight. While heavy snow is also possible with this trough, the
heaviest snowfall rates are expected to remain within the Cascades
northward into the western Puget Sound and adjacent Olympic
Peninsula.
..Wendt.. 02/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PQR...
LAT...LON 44962350 45882353 45962340 45972315 45762290 45452279
44872297 44622317 44582338 44732347 44962350Nearby
Mesoscale Discussions in Oregon, 2021Every mesoscale discussion in 2021
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.