USGS--Drought Status Report 12-07-01--Virginia

A strong and persistent high pressure system has been in place since the middle part of October preventing significant moisture from moving northeast over the state of Virginia from the Gulf of Mexico. As a result, cold fronts crossing the region have been moisture starved and producing little or no precipitation. This trend is expected to continue as another semi-dry cold front crosses the state on 12/7 - 12/8. This is only expected to produce a few hundredths of an inch at best as the front becomes more parallel to the east to west upper flow. The front will likely stall near the Virginia and North Carolina border and a weak disturbance will move along the front but again expected to produce little as most of the rainfall will be near the southeastern portion of the state. After this one-shot rain, high pressure will once again take over and usher in cooler and drier air 12/9 - 12/10 and a moderation of temperatures through 12/13. At any rate, there are no indications that the long-wave weather pattern will change over the next 7-10 days.

The 30-day outlook generally calls for normal temperatures and normal precipitation. The 90-day outlook calls for normal temperatures and precipitation.

Note: The latest Drought Monitor (dated December 4, 2001) is attached to this report.

REPORT OF THE STATE CLIMATOLOGIST- December 7, 2001

In general, Virginia dryness has increased at a moderate pace since the last report of the Drought Task Force. Recent shortfalls in rain have become even larger, and much above-normal temperatures have increased evaporation to rates normally seen in early October.

As can be seen in the attached table, November rainfall averaged a mere 22% of the long-term mean across the state. Totals ranged from 15% of normal in both the eastern and western Piedmont, to 23% of normal in Northern Virginia. Although the final ranking is not yet available from the National Climatic Data Center, November will likely be around the fifth driest in the 107-year Virginia history.

October was the fourth driest on record. In combination, therefore, it seems very likely that the consecutive nature of these two very dry months will place this October-November as either the driest or second driest in our record. However, the final November numbers will not be in until next week, so it is advisable to wait until then before reporting this in the media.

Percent-of-normal rain figures are less striking when considering the last six months. June-November has averaged 77% of normal rain statewide, ranging from 62% of normal in the western Piedmont to 88% of normal in Tidewater. On a 12-month basis, the state is averaging 81% of normal. The six and 12-month totals reflect the relatively wet early summer and late winter of 2001. For comparative purposes, the smallest 12-month totals in the major 1998-99 drought were 55-65% of normal. Some combined effects of that drought, along with the current one, are evident in very low levels in benchmark wells, such as Tyler in Louisa County. Although that data requires some extrapolation, it does not yet appear to be as low as it would have been in the prolonged and severe drought of the mid-1960's.

In summary, the current drought remains rather short in duration, but very sharp in magnitude. This is reflected in Palmer Drought Severity Index values, which indicate moderate drought in Tidewater, the eastern and western Piedmont, and the Shenandoah Valley/Western Mountain regions. Northern and Southwestern Virginia do not yet register moderate drought on this index, which probably reflects a systematic problem with this index-particularly in the winter, it can be very slow to declare a drought.

As of this writing (December 7), there appears to be an increasing prospect for a moderate statewide rain in the next 60 hours, which would dramatically reduce near-surface dryness and lower the threat of fire.

The current drought is being caused by an unusual extension of subtropical high pressure over the Gulf of Mexico. The cause for this phenomenon is unknown, but all the dynamic long-range forecasting models indicate it will tend to persist. Hence, the long-range picture remains disturbingly dry.

PROVISIONAL ASSESSMENT OF HYDROLOGIC CONDITIONS IN VIRGINIA, December 06, 2001

Recent lack of precipitation has caused streamflow across the State to decline well below the normal range for December. Streamflows are below the normal range in every major basin within the State and new record lows for December are being observed at gages in the York, James, and Roanoke River Basins.

During the fall months, ET (evaporation and transpiration) and precipitation normally are low. Streamflows usually decline to their lowest levels in September or October with a slight increase in flow in November and December. Therefore, the normal range of flow for November and December is greater than the normal range of flow for September and October. Because streamflows have remained fairly constant and the normal range of flows has increased, current streamflows are statistically lower than they were in November, even though the flows are very similar.

Data are provisional and subject to revision. Streamflow values are in cubic feet per second (cfs). The normal range of flow is defined as flows between those equaled or exceeded 75% of the time and those equaled or exceeded 25% of the time on the flow duration curve. A flow duration curve shows the percentage of time a particular flow occurred during the available period of record. The last column in the table relates the current flow to the monthly flow duration curve for that site. At the South River near Waynesboro, for example, current (Dec. 06) flow of 29 cfs has been equaled or exceeded 95% of the time in November.

	PRECIPITATION SUMMARY		Dec. 7, 2001

CD	DEC-NOV	DEC-NOV	DEC-NOV	DEC-NOV
	2000-2001	NORMAL	DEPARTURE	% DEPART.
1	35.9	43.7	-7.8	82%
2	33.2	43.3	-10.1	77%
3	32.6	44.8	-12.2	73%
4	36.3	40.8	-4.5	89%
5	30.7	39.4	-8.7	78%
6	36.8	43.3	-6.5	85%
Statewide	34.3	42.4	-8.1	81%


CD	JUN-NOV	JUN-NOV	JUN-NOV	JUN-NOV
	2001	NORMAL	DEPARTURE	% DEPART.
1	19.9	22.6	-2.7	88%
2	15.9	22.6	-6.7	70%
3	14.5	23.4	-8.9	62%
4	18.2	22.0	-3.8	83%
5	14.6	21.2	-6.6	69%
6	18.4	22.1	-3.7	83%
Statewide	17.0	22.1	-5.1	77%


CD	SEP-NOV	SEP-NOV	SEP-NOV	SEP-NOV
	2001	NORMAL	DEPARTURE	% DEPART.
1	5.0	10.1	-5.1	50%
2	2.8	10.6	-7.8	26%
3	3.9	11.1	-7.2	35%
4	3.7	10.6	-6.9	35%
5	3.5	10.3	-6.8	34%
6	3.8	10.2	-6.4	37%
Statewide	3.8	9.2	-5.4	41%


CD	OCT-NOV	OCT-NOV	OCT-NOV	OCT-NOV
	2001	NORMAL	DEPARTURE	% DEPART.
1	1.6	6.3	-4.7	26%
2	1.0	7.2	-6.2	14%
3	1.6	7.4	-5.8	22%
4	1.6	7.1	-5.5	23%
5	1.6	6.9	-5.3	23%
6	1.7	6.7	-5.0	25%
Statewide	1.5	5.8	-4.3	26%


CD	NOV	NOV	NOV	NOV
	2001	NORMAL	DEPARTURE	% DEPART.
1	0.6	3.1	-2.5	19%
2	0.5	3.4	-2.9	15%
3	0.5	3.4	-2.9	15%
4	0.8	3.5	-2.7	23%
5	0.6	3.2	-2.6	19%
6	0.7	3.2	-2.5	22%
Statewide	0.6	2.7	-2.1	22%

	HISTORICAL CONDITIONS (FOR AVAILABLE PERIOD OF RECORD)				CURRENT CONDITIONS (DEC. 06, 2001)
	MINIMUM DAILY MEAN FLOW(cfs)	MINIMUM DAILY MEAN FLOW FOR DEC. (cfs)	NORMAL RANGE OF FLOW FOR DEC. (cfs)	MEDIAN FLOW FOR DEC. (cfs)	FLOW (cfs)	FLOW DURATION (% OF TIME CURRENT FLOW EQUALED OR EXCEEDED)
SHENANDOAH RIVER BASIN
South River near Waynesboro, Va.	17	23	53-157	101	29	95
South Fork Shenandoah River at Front Royal, Va.	107	162	547-1,596	1,010	284	>95
North Fork Shenandoah River at Cootes Store, Va.	0.2	2.9	28-171	75	10	85
North Fork Shenandoah River near Strasburg, Va.	35	50	170-572	312	93	95

POTOMAC RIVER BASIN
Goose Creek near Leesburg, Va.	0.4	4.6	73-355	174	28	93

RAPPAHANNOCK RIVER BASIN
Rappahannock River at Remington, Va.	2.9	35	265-812	466	117	95
Rapidan River near Culpeper, Va.	2.2	20	218-615	379	80	>95

YORK RIVER BASIN
Pamunkey River near Hanover, Va.*	47	105	399-1,167	673	95	>95
Mattaponi River near Beulahville, Va.	.78	52	281-762	449	55	>95
JAMES RIVER BASIN
Jackson River near Bacova, Va.	13	20	61-184	106	16	>95
Potts Creek near Covington, Va.	15	15	52-181	100	32	90
Cowpasture River near Clifton Forge, Va.	40	60	171-566	305	70	>95
Craig Creek at Parr, Va.	25	35	105-416	220	53	95
James River at Buchanan, Va.*	257	316	731-2,623	1,400	453