July 2013

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - During the previous two weeks, unseasonable rainfall overspread the Pacific Northwest and northern California. Showers and thunderstorms over western Texas brought localized drought relief, but mostly dry conditions persisted across eastern Texas and the Southwest. Heavy rainfall during late June eased drought across the upper Midwest, while moderate drought conditions lingered over northern Minnesota. During July, robust monsoon thunderstorm activity is forecasted to bring drought relief to southern Colorado, most of New Mexico, western Texas, and eastern Arizona, but may cause localized flash flooding in wildfire burn scar areas. In contrast, a hot, dry start to the month is expected to exacerbate drought conditions in the desert Southwest and the northern Rockies. Summer convection is forecasted to ease drought conditions in eastern Texas and far eastern Kansas, while prospects for drought improvement are less certain across the remainder of the Plains. Drought persistence is also forecasted for northern Minnesota, which missed out on recent rainfall, while widespread heavy rainfall expected in early June is likely to remove lingering drought in the central Appalachians. Seasonable dryness and suppressed tropical convection favor drought persistence and possible expansion across Hawaii, while drought conditions are likely to persist in central Alaska, where record breaking temperatures were observed in late June.

Tools used in the monthly U.S. Drought Outlook (MDO) included the official CPC temperature and precipitation outlooks for July 2013, various short- and medium-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, dynamical models (CFSv2, NMME, and IMME), the 384-hour total precipitation forecasts from several runs of the GFS, the 7-day quantitative precipitation forecast from the NCEP Weather Prediction Center, climatology, and initial conditions. As of June, we remain in ENSO Neutral conditions, with the convectively active phase of a coherent MJO pattern located over the tropical Western Hemisphere.

Mostly dry weather dominated the monsoon regions of the southwestern U.S. during the previous two weeks, with much above normal temperatures exacerbating wildfire conditions in Colorado and New Mexico. The short term forecast depicts an unusually amplified upper-level pattern for early July, with troughing over the south-central U.S. retrograding westward, promoting easterly flow. Ensemble forecasts depict the formation of a heat low near the California and Nevada border, with high pressure centered over Colorado and New Mexico. These factors are expected to promote moisture advection and thunderstorm development over the eastern monsoon regions of the southern Rockies and High Plains. The WPC 7-day precipitation forecast and the GFS both predict an area of locally heavy rainfall straddling the border of Colorado and New Mexico, with accumulation totals near an inch expected as far south as the Trans-Pecos region of Texas. In contrast, mostly dry weather and excessive heat are expected during the upcoming week across much of Arizona, Nevada, and southern California. Although the CFSv2 depicts wet anomalies over Arizona and the current MJO phase is favorable for the promotion of Gulf moisture surges, the prospects of overcoming the currently worsening drought situation in the desert Southwest is uncertain. The CPC updated July outlook places the highest probabilities of above-median precipitation over New Mexico, eastern Arizona, and far western Texas, with equal chances of below, near, and above-median precipitation over southern Nevada. Therefore, drought persistence is forecasted for southern California, Nevada, and western Arizona. Improvement and removal of shallow drought is anticipated across eastern Arizona, New Mexico, southern and central Colorado, and western Texas.
Forecast confidence for the monsoon regions of the southwestern U.S. is moderate.

Unseasonable precipitation and below average temperatures overspread northern California during the previous week, while little rainfall was observed east of the Sierras over the Great Basin. July is a climatologically dry month for these regions, as monsoon thunderstorms generally remain to the east and south. CPC's 8-14 day outlook tilts the odds towards above-median precipitation over Utah and eastern Nevada, but the updated July outlook maintains equal chances of below, near, or above-median precipitation. Above normal temperatures are expected across California and the Great Basin during the upcoming two weeks, promoting enhanced evapotranspiration, and the CPC updated July outlook also tilts the odds towards above median temperatures. Based on the dry climatology and forecasts of above normal temperatures, drought persistence is favored across California and the Great Basin.
Forecast confidence for California and the Great Basin is moderate to high.

A strong trough of low pressure brought much above normal precipitation and below normal temperatures to the Northwest, with the highest precipitation anomalies observed across Washington, Oregon, and western Idaho. In contrast, below average precipitation lingered across southeastern Idaho, southern Montana, and most of Wyoming during the previous two weeks. While widely scattered showers are expected over parts of the Northwest during the upcoming week, a building ridge of high pressure will promote much above normal temperatures. CPC's 8-14 and updated July outlooks both tilt the odds towards below median precipitation over Washington and northern Idaho, with above median temperatures also favored. July is also a climatologically dry time of year for the Northwest. Therefore, drought persistence is expected for the Northwest, particularly over the portions of the northern Rockies that missed out on last week's rainfall. Drought expansion is possible across abnormally dry portions of Idaho, southwestern Montana, and northwestern Wyoming.
Forecast confidence for the Northwest is moderate.

Scattered showers and thunderstorms developed over western Texas during the previous week, bringing localized drought relief and greening of range lands. In contrast, mostly dry weather and hot temperatures were observed over eastern Texas and central Oklahoma. During the upcoming week, showers and thunderstorms are likely, with the highest rainfall amounts expected over western Texas and the northern Texas Panhandle as monsoon moisture spills onto the Plains. The CPC 8-14 day outlook shows enhanced odds of above-median rainfall over northeastern Texas, as a retrograding trough of low pressure is expected to promote convective activity. The CFSv2, in contrast, forecasts abnormal dryness across much of eastern Texas during July. The CPC updated July outlook maintains equal chances of below, near, and above-median precipitation for central and eastern Texas. Based on these forecasts, drought improvement and removal of shallow drought is forecasted for the eastern edges of the drought areas of Texas and along the northeastern Gulf coast, while drought persistence is favored for central and southern Texas and Oklahoma.
Forecast confidence for the Southern Plains is moderate.

Widespread heavy rainfall overspread the upper Midwest, but largely missed a region of moderate drought in northern Minnesota. Generally quiet weather was observed across the northern and central Plains, where convection was more of a hit or miss variety. Mostly dry weather is expected along the Great Plains during the upcoming week, and showers across the upper Midwest are expected to produce accumulations generally under a half inch. The CPC 8-14 day outlook forecasts enhanced chances of below median precipitation and above median temperatures over the northern Plains and upper Midwest, while the CPC updated July outlook maintains equal chances of below, near, or above-median temperatures and precipitation. Although July is a wet time of year for northern Minnesota, it is unlikely that drought will be removed based on the dry initial conditions and the expected drier than normal start to the month. Drought persistence is forecasted for the central Plains, although the NAEFS model indicates the possibility of substantial rainfall pushing as far west as eastern Kansas, which may reach areas experiencing long term moderate drought conditions.
Forecast confidence for the northern and central Plains and the upper Midwest is moderate.

Mostly quiet weather overspread the mid-Atlantic states during late June, with increased thunderstorm activity developing late in the period. During early July, a persistent southerly flow on the east side of an amplified trough will promote continued widespread daily thunderstorm activity, with heavy rainfall accumulations expected. The CPC updated July outlook tilts the odds towards above median precipitation across the southeastern and east central U.S. Based on these outlooks, it is likely that the small area of lingering drought near the southwest corner of Pennsylvania will be removed by the end of the month.
Forecast confidence for the central Appalachians is high.

Dry weather and record breaking heat exacerbated drought conditions over central Alaska during the previous two weeks. Mostly dry weather is expected to continue during the upcoming week. The CPC 8-14 day outlook shows no tilt in the climate anomalies, and the July outlook maintains equal chances of below, near, and above normal precipitation. Based on the dry initial conditions, however, drought persistence is expected for central Alaska.
Forecast confidence for Alaska is moderate.

July is climatologically dry across the Hawaiian Islands. Additionally, the suppressed convective phase of the MJO is currently propagating eastward over the tropical Pacific, which is expected to contribute to below average precipitation over Hawaii. Sea surface temperatures surrounding the islands have decreased and are near normal. Based on these factors, drought persistence is expected for Hawaii, with additional development possible in areas that are abnormally dry.
Forecast confidence for Hawaii is high.