National Weather Service United States Department of Commerce

Remnants of Arthur and Heavy Rainfall Across the South; Fire Weather Threat in the West

Life-threatening, potentially catastrophic flash flooding expected along the central Gulf Coast as the remnants of Arthur track across the area. Isolated brief tornadoes and damaging gusts remain possible overnight in the Southeast. Isolated to scattered dry thunderstorms may cause lightning-ignited fires and erratic behavior due to gusty winds across parts of the West Friday. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260619_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 06/19 00Z 1.11 2523  82  80  12 0.00
Fri 06/19 01Z 1.53 2527  79  77  11 0.00
Fri 06/19 02Z 2.66 2532  76  81  10 0.00
Fri 06/19 03Z 2.84 2535  82  66   9 0.00
Fri 06/19 04Z 2.21 2537  87  74   9 0.01
Fri 06/19 05Z 1.74 2537  92  75   8 0.02
Fri 06/19 06Z 1.35 2636  94  77   8 0.04
Fri 06/19 07Z 1.17 2635  95  75   8 0.04
Fri 06/19 08Z 1.10 2635  95  71   8 0.02
Fri 06/19 09Z 1.05 2734  96  68   8 0.03
Fri 06/19 10Z 1.05 2734  93  60   8 0.02
Fri 06/19 11Z 0.99 2734  90  59   8 0.01
Fri 06/19 12Z 0.99 2734  89  61   8 0.00
Fri 06/19 13Z 1.02 2733  90  61   8 0.00
Fri 06/19 14Z 1.05 2729  92  58   8 0.01
Fri 06/19 15Z 1.19 2727  94  57   8 0.01
Fri 06/19 16Z 1.49 2626  94  70   8 0.01
Fri 06/19 17Z 2.69 2626  94  70   8 0.01
Fri 06/19 18Z 6.93 2625  92  75   9 0.01
Fri 06/19 19Z 9.59 2724  89  75   9 0.00
Fri 06/19 20Z 6.64 2624  89  61  10 0.00
Fri 06/19 21Z 10.05 2625  82  52  10 0.00
Fri 06/19 22Z 14.33 2627  75  49  10 0.00
Fri 06/19 23Z 6.70 2629  79  47   9 0.00
Sat 06/20 00Z 2.55 2630  84  50   9 0.00
Sat 06/20 01Z 1.51 2732  92  66   8 0.02
Sat 06/20 02Z 1.04 2829  93  77   8 0.06
Sat 06/20 03Z 0.98 2828  97  83   8 0.05
Sat 06/20 04Z 0.92 2827  97  79   8 0.09
Sat 06/20 05Z 0.89 2827  97  81   7 0.07
Sat 06/20 06Z 0.87 2727  97  80   7 0.06
Sat 06/20 07Z 0.81 2828  96  89   8 0.05
Sat 06/20 08Z 0.76 2828  97  88   8 0.05
Sat 06/20 09Z 0.62 3028  97  87   7 0.05
Sat 06/20 10Z 0.56 3026  98  86   7 0.05
Sat 06/20 11Z 0.47 3125  97  82   6 0.02
Sat 06/20 12Z 0.40 3224  98  89   6 0.03
Sat 06/20 13Z 0.45 3224  98  90   6 0.03
Sat 06/20 14Z 0.50 3124  97  79   6 0.03
Sat 06/20 15Z 0.58 3122  95  64   6 0.01
Sat 06/20 16Z 1.17 3119  95  66   6 0.00
Sat 06/20 17Z 1.75 3118  93  70   7 0.01
Sat 06/20 18Z 1.92 3117  92  70   7 0.01
Sat 06/20 19Z 1.46 3017  93  68   8 0.01
Sat 06/20 20Z 0.92 3017  91  57   8 0.01
Sat 06/20 21Z 0.65 3017  90  44   8 0.00
Sat 06/20 22Z 0.58 3017  88  41   9 0.00
Sat 06/20 23Z 0.49 3117  75  45  10 0.00
Sun 06/21 00Z 0.52 3018  76  48  10 0.00
Sun 06/21 01Z 0.55 2918  88  49  10 0.00
Sun 06/21 02Z 0.55 2820  90  51  10 0.00
Sun 06/21 03Z 0.51 2920  89  52  10 0.01
Sun 06/21 04Z 0.46 2919  87  55  10 0.00
Sun 06/21 05Z 0.43 2918  86  58  10 0.00
Sun 06/21 06Z 0.40 2918  85  63  10 0.00
Sun 06/21 07Z 0.36 3017  85  62  10 0.00
Sun 06/21 08Z 0.31 3016  85  64  10 0.00
Sun 06/21 09Z 0.31 3016  88  67   9 0.00
Sun 06/21 10Z 0.34 3017  90  71   9 0.00
Sun 06/21 11Z 0.32 3016  88  70   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.96 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1