Hydrologic Outlook – An Anomalously Warm And Increasingly Unstable Atmosphere Will Have To Be Closely Monitored For Additional Waves Of Heavy Rainfall In Coming Days
Although the chance for showers & thunderstorms will increase by mid-week ( Wednesday – February 21 ), and should be closely monitored, the highest risk for more heavy to excessive rainfall is currently timed for the February 24-25 period. Stay tuned for updates.
Monday Night Into Tuesday Morning
Partly-mostly cloudy. Windy. S-SSW winds 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet. SSW-SW winds 15-25 mph, with higher gusts, along mountain ridges above 2700 feet. Mild with temperatures widespread from low 50s to low 60s ( mid-upper 40s in coolest valley locations ).
Tuesday Afternoon
Partly-mostly sunny. Unseasonably warm. Windy. Winds S-SW at 10-20 mph, with higher gusts. Temps varying from mid-upper 50s in upper elevations to the low-mid 70s.
Tuesday Night Into Wednesday Morning
Partly-mostly cloudy. Windy. SSE-SSW winds 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet. SSW-SW winds 15-25 mph, with higher gusts, on mountain ridges above 2700 feet. Mild with widespread temperatures in the 50s.
Wednesday Afternoon
Mostly cloudy. A chance of showers & thunderstorms. Downpours possible. SSW-SW winds 5-15 mph, with higher gusts. Temperatures varying from 50s in upper elevations to the upper 60s to lower 70s.
Wednesday Night Into Thursday
Mostly cloudy. A chance of showers & thunderstorms. Winds SSW-SW at 5-15 mph, with higher gusts, along middle-upper elevation mountain ridges. Mild with widespread temps in the 50s to near 60 degrees.
Up to 73.0″ of snow ( at least, and likely more ) fell at the summit level of the High Knob Massif during February 2015 as a huge snowpack ( 3 to 4+ feet ) developed this week only three years ago. Air temps dropped to -23 degrees below 0 in Clintwood into morning hours of February 20, and very likely to below -30 degrees in high valleys of the massif ( * ).
*This was prior to the beginning of high-resolution data collection in high valleys of the massif as part of UVA-Wise undergraduate field research; however, observed differences between Clintwood and high valleys since that time suggests MIN temps would have easily been colder than -30 degrees below zero.
Black Mountain Mesonet During February 1-18, 2018
Although just over a foot of snow has fallen at the summit level of the High Knob Massif this month, it has really been all about heavy to excessive rainfall with a general 11.00″ to 13.00″+ observed in upper elevations above 3000 feet from the High Knob high country to the crest of Black Mountain.
A total of 7.68″ being measured in Clintwood ( just shy of the 8.08″ record established during February 2003 ).
Blacksburg NWS Climate Data During February 1-19, 2018
Precipitation measured during Winter 2017-18, and this month, has been FAR from even across southwest Virginia as is so often the case ( it is part of long-term climatology ).
Bluefield NWS Climate Data During February 1-19, 2018
And it is not just due to Blacksburg being located within the valley of the New River, but also includes sites at the top of the plateau ( such as Bluefield ).
Totals of 6.63″ to 7.09″ in Blacksburg-Bluefield since the start of Meteorological Winter ( December 1, 2017 ) versus general totals of 21.00″ to 22.00″+ in the High Knob Massif during this same time.
925 MB Mean Flow Vector During February 1-17, 2018
It is a true orographic rain shadow effect, but along an axis that is oriented differently than textbook cases. During February, above, low-level air flowing into the High Knob Massif has arrived via the open expanse of the Tennessee Valley versus locations to the east in southwest Virginia where a SSW flow has to first cross the long axis of the TN-NC border, and SW North Carolina, where moisture extraction occurs. Looking at the entire winter season ( below ) a WSW component in low-levels means air must first cross the High Knob Massif and Cumberland Mountains before reaching locatons farther east in southwestern Virginia. Again, a shadowing effect.
Composite mean flow vectors reveal part of the reason as to why there is such a HUGE difference in precipitation across southwestern Virginia, between the High Knob Massif and sites farther east, with low-level 925 MB flow observed in February ( above ) and since the start of winter ( below ).
925 MB Mean Flow Vector From Dec 1, 2017 to Feb 17, 2018
With a FOOT or more of precipitation already accumulated at upper elevations, it now is only a matter of how high will totals get before this month finally ends ( lets all hope and pray it can end without any more serious high water issues ).
Looking Ahead: Late Week-Weekend
There is significant concern for later this week. While many love warm weather, it is February and record level warmth is seldom ever a good thing in winter since it is a signal that the atmosphere is greatly out of balance and will be working to restore the balance ( the restoration of such being the problem since that = more rain upcoming ).
GFS Model Total Precipitation Through Weekend
Since the GFS Model has recently been closest to actual rain amounts ( although it too under-estimated totals ), I will use it for a look ahead at possible rain yet to come through this weekend ( the GFS 21-Member Ensemble Mean is below ).
With the first CAPE of this year showing up in models, a concern is that thunderstorms will develop and/or become embedded within a rain shield to enhance amounts and the downpour potential.
GFS 21-Member Ensemble Mean Total Precipitation Through Weekend
This run of the GFS Model group shows that the operational run is pretty much in agreement with the 21-Member Ensemble Mean.
Upper-level Water Vapor Image From GOES-16
From low to upper levels a notable tropical connection is very visible on GOES-16 images ( an atmospheric river of moisture that needs only a focus to trigger release of its tremendous latent energy ).
Increased amplitude of the flow pattern shows up well on this 500 MB Earth View ( at link ), with a High pressure off the southeastern USA coast anchoring the flux of warm, moist air into the central-eastern USA.
Emergency Managers as well as everyone living along creeks and typical poor drainage, flood prone locales, will need to increase alert levels in coming days.
