Two
fast-moving storms impacted the Lower 48 last week. Heavy rain fell
across parts of the Midwest and South, leading to broad areas of drought
improvement in these regions. Parts of the West saw much-needed
rainfall. In most cases, these amounts were not enough to bring relief
to the region’s relentless long-term drought conditions. Pockets of
dryness also continued across the northern High Plains, South, and
Southeast leading to drought expansion.
Long-term
drought has been slow to improve in the Northeast despite recent rains
and cool weather. Abnormal dryness (D0) improved across parts of Maine,
New Hampshire and Vermont, where above-normal precipitation helped
improve moisture deficits. Stream flows are near- to above-normal and
soil moisture indicators show improvement. Other areas of improvement
include parts of the Delmarva Peninsula where recent rains eliminated
short-term abnormal dryness (D0). Abnormal dryness expanded over parts
of West Virginia and western Maryland where precipitation deficits,
stream flow measurements and soil moisture conditions have fallen below
normal.
The
southeast saw a mix of improvements and worsening short-term drought
conditions. Rainfall totals from 1.5 to more than 3 inches brought
relief to moderate drought in parts of coastal South Carolina and
abnormally dry areas in North Carolina, Alabama and near the
Georgia-Florida border. Precipitation indicators and stream flow
measurements show improvements in these areas. Moderate drought expanded
across a large swath of southern Georgia, an area that has continued to
miss out on surplus rainfall. Pockets of abnormal dryness and/or
drought expanded in consistently dry areas of North and South Carolina
and southwest Alabama. Indicators supporting drought expansion in the
southeast include 60-to-90-day precipitation deficits, declining soil
moisture and below-normal stream flow.
This
week the South saw drought worsen across west and south Texas and the
Oklahoma Panhandle. Above-normal temperatures combined with below-normal
precipitation and high winds exacerbated conditions. Drought indicators
supporting the degradations include increasing precipitation deficits,
dry surface and root zone soil moisture and low stream flow. State
drought teams noted reports of blowing dust and crop failures in the
area. Drought also expanded across southern Louisiana. This area has
been in severe drought (D2) since March without any relief in weeks.
One-category improvements were made to drought conditions across east
Texas, southern Arkansas, north and central Louisiana and Mississippi in
areas where the heaviest rain (3 inches or more) fell and where
warranted by short-term precipitation indicators, streamflow, soil
moisture and other measures.
Above-normal
precipitation combined with below temperatures led to improvements
across much of the Midwest this week. Until recently, the region hadn’t
had enough precipitation to warrant improvements to deficits that had
been building since spring last year. Now, virtually all short-term
drought has been eliminated. This is denoted by the removal of the S
designation on the map. Long-term drought remains where precipitation
deficits of 6 months or longer exist and where deeper soil moisture and
groundwater indicators have yet to recover.
Much
of the High Plains remained dry last week resulting in deteriorating
drought conditions across parts of the Dakotas and Nebraska. The eastern
edges of abnormal dryness (D0) and moderate drought (D1) crept
eastward. Severe drought (D2) expanded over a large swath from southwest
North Dakota to central Nebraska. Extreme drought spread in central
Nebraska. Short-term dryness is superimposed over long-term moisture
deficits across the region. The lack of seasonal snow cover combined
with the onset of spring has people in the region worried. Soil moisture
is very low, stream flows continue to decline and state reports
indicate that stock ponds are drying up.
Parts
of the West saw much needed precipitation with rain over the West Coast
and higher elevation snow over the Sierra Nevada Mountains. In most
cases, these amounts were not enough to bring relief to drought
conditions that have plagued the region for months. Only western Oregon
saw minor improvements to abnormal dryness (D0) and moderate drought
(D1) in response to recent precipitation. Across much of the West,
higher than normal temperatures last week caused premature snow melt,
with snowpack values plummeting over just a few days. The California
Department of Water Resources noted that about one-third of the water
equivalency disappeared in a week. Extreme drought (D3) expanded in
northern California, parts of Utah, and New Mexico. In these locations,
the warm weather has led to increased evaporative demand and stress on
vegetation. The rest of the West remained unchanged this week.
In
Puerto Rico, abnormal dryness (D0) expanded as precipitation deficits
began to build and soil moisture, streamflow, and well data showed
declining values.
A dry upper-level ridge
inhibited precipitation across the U.S. Virgin Islands (USVI) during
this USDM week (March 23-29). But enough moisture lingered over the
region to support the development of showers triggered by afternoon
heating. Satellite and radar-based analyses indicated less than half an
inch of precipitation fell across the islands. Groundwater levels
continued to fall on St. John and St. Croix, but leveled off on St.
Thomas. A cold front was approaching the region as the week ended.
Above-normal rainfall this week improved the drought status on St.
Thomas, but no change was made to the depiction on St. Croix or St.
John.
On St. John, 7-day rain gauge totals
were about a third of an inch. This is below the weekly long-term
average computed for the station at Windswept Beach. Month-to-date
rainfall totals at the CoCoRaHS stations ranged from 2.08 inches to 2.57
inches. The Standardized Precipitation Index (SPI) was at D1 levels at
the 6-month time scale. The groundwater level at the USGS Susannaberg
DPW 3 Well at St. John has steadily declined over the last month, and
continued to decline this week, with depth to water at 19.16 feet, which
is the lowest level since 2017. D1-L continued for St. John.
Seven-day
precipitation totals at CoCoRaHS stations on St. Thomas ranged from
0.16 inch to 0.72 inch. King AP recorded 0.61 inch, which is above
normal. Monthly totals ranged from 1.65 inches to 3.74 inches. The
value of 2.67 inches at King AP was 155% of normal for the
month-to-date. The SPI at King AP was at D1 levels for the last 6 to 12
months. The rainfall total since the last big wet season system
(8/25-3/28) is 17.14 inches, which is ninth driest for the period (16th
percentile). The groundwater level at the USGS Grade School 3 Well at
St. Thomas has held steady over the last week after steadily declining
over the last month. D2-L was improved to D1-L for St. Thomas this week
due to above-normal rainfall and moderating groundwater levels.
The
CoCoRaHS weekly precipitation totals on St. Croix ranged from 0.13 to
0.86 inch, with about half of them below a third of an inch and half
above. Month-to-date totals at the CoCoRaHS stations ranged from 2.13
to 3.69 inches, with most below 3.00 inches. The weather station at
East Hill had 0.17 inch for the week, which is below normal, but 2.76
inches for the month to date, which is 193% of normal. Rohlsen AP
reported 0.01 inch for the week and 0.81 inch for the month. The weekly
total was below normal, and the monthly total was 54% of normal. The
rainfall total since the last big wet season system (8/25-3/20) is 16.24
inches, which is 8th driest for the period (13th percentile). The SPI
at Rohlsen AP and East Hill was in the D1 range at the 6- to 12-month
time scales. The groundwater level at the USGS Adventure 28 Well at St.
Croix has steadily declined over the last year, and continued to
decline this week, with depth to water at 31.12 feet, which is the
lowest level in the 2016-present record. D2-L continued for St. Croix.
Alaska remained free of drought or abnormal dryness this week.
In
Hawaii, Enhanced trade wind rainfall and thunderstorms last week
brought much needed rainfall to some parts of the state. While this
eased some windward drought, the leeward areas did not get much
rainfall. As a result, drought has worsened on portions of the Big
Island and Maui. On the Big Island, moderate (D1) and extreme (D3)
drought expanded. Satellite data and rancher reports indicate extremely
poor pasture conditions. In Maui, extreme drought (D3) expanded. In
contrast, wet conditions in the middle of the week helped ease drought
conditions along the windward slopes of Oahu and Kauai.
Several
tropical weather features brought rain to parts of Micronesia during
this USDM week (March 23-29). These included Inter-Tropical Convergence
Zone (ITCZ) convection in the east, a near-equatorial trough in the
west, and weak trade-wind troughs. An upper-level low, or TUTT cell,
migrated westward across northern portions of the region; it enhanced
showers over the Marshall Islands. The TUTT cell, along with a surface
trough and cold front/shear line, triggered showers near the Marianas,
but these systems did not produce much rain as they moved across the
Marianas. Showers associated with the South Pacific Convergence Zone
(SPCZ) moved northward across the Samoan Islands, giving Tutuila a wet
week. Satellite-based analyses of 7-day precipitation (QPE) showed a
band of 2+ inches of rain that stretched from the southern Marshall
Islands (RMI) westward across the Federated States of Micronesia (FSM)
to the Republic of Palau. Lesser amounts fell north and south of this
band. The satellite QPE indicated over an inch of rain fell over
Tutuila. Conditions improved with abnormal dryness ending in the
southern RMI and northern Chuuk State, but abnormal dryness returned in
southern Pohnpei State.
The week was wet in
Palau and American Samoa. The weekly minimum precipitation required to
meet most water needs is 2 inches in Palau and 1 inch in American Samoa.
Airai received 1.92 inches for the week but Koror COOP station
recorded 2.70 inches, and both stations had more than the monthly
minimum of 8 inches, so D-Nothing continued in Palau. Pago Pago (2.80
inches) and the automated stations at Siufaga Ridge (2.16) and Toa Ridge
(1.74) had more than the 1-inch weekly minimum, and all 3 stations were
above the monthly minimum to date, so D-Nothing continued for Tutuila.
In
the Marianas, less than half an inch of rain was recorded this week at
Rota (0.23) and Saipan (0.17 inch at the ASOS gauge, 0.33 at the IAP,
and 0.39 at the NPS station) and less than an inch fell at Guam (0.83).
The weekly minimum is 1 inch for the Marianas. The month-to-date
totals at Guam (1.82) and Rota (1.91) were below the monthly minimum for
this time in the month. Reports indicate vegetation on Guam was brown
in some areas but green in others, and wildfires have been fairly common
in the hills of southern Guam. The KBDI (a fire drought index) reached
into the extreme category (with a value of 738) by the end of the USDM
week. Dry air, a high KBDI, and strong winds associated with the cold
front/shear line created critical fire weather conditions on Guam,
triggering the issuance of a fire weather watch and Red Flag Warning.
D1-S continued on Guam and D0-S continued on Rota and Saipan.
In
the FSM, weekly rain gauge totals in the ITCZ rainfall band ranged from
3.84 inches at Woleai to 6.05 inches at Nukuoro. D-Nothing continued
at the locations within the band. To the south, Kapingamarangi had no
measurable rain this week; with the last 3 weeks dry, D0-S was
introduced at Kapingamarangi. To the north, Chuuk recorded 1.65 inches
of rain this week, but had very wet conditions the 3 previous weeks and a
wet month (13.36 inches for March so far), so D0-S ended. With a third
of an inch of rain (based on data received) for the week and only 4.89
inches for the month, D1-S continued at Fananu. D0-S continued at Yap,
which received 0.64 inch of rain this week, and Ulithi (0.81 inch).
Lukunor had a dry week (0.59 inch) but a wet month-to-date (7.75
inches), so D-Nothing continued.
The southern
Marshall Islands were in the wet ITCZ band, while the northern Marshalls
were mostly dry. Wotje received 0.75 inch of rain for the week and
2.55 inches for the month so far, both of which are below their
respective minimums. D3-SL continued for Wotje. D0-S ended at
Kwajalein and Majuro, where the weekly rainfall totals were 3.87 and
7.26 inches, respectively, and month-to-date totals were 11.07 and 17.30
inches, respectively. With weekly totals over 3 inches, D-Nothing
continued at Ailinglaplap (5.57 inches of rain for the week), Jaluit
(7.35), and Mili (3.51). Monthly rainfall totals were over 15 inches at
these three stations.
Looking Ahead
The
National Weather Service Weather Prediction Center forecast (valid
March 31 – April 7) calls for heavy rain and storms ahead of an
advancing cold front extending from south of Lake Michigan to East
Texas. Storms will progress eastward through the remainder of the week.
The Northern Plains, Upper Midwest, and New England can expect
snow/freezing rain. Heavy rain and mountain snow are expected from the
Pacific Northwest to the Rockies. Moving into next week, the Climate
Prediction Center Outlook (Valid April 7 – 13) favors above normal
temperature for a large part of the West, extending from California
across the Great Basin and into the southern Rockies. Meanwhile, near to
above normal temperatures are favored for the Northeast and Eastern
Seaboard. Below normal temperatures are expected over the eastern
central CONUS. The outlook favors above normal precipitation across much
of the northern tier of the Lower 48 and Alaska. Near to below normal
precipitation is favored over southern areas of the West and the
Southern and Central Plains.