NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260829_1800
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)
=== ===== === ==== ==== === === === ====
Sat 08/29 18Z 3.75 2706  81  10   8 0.00
Sat 08/29 19Z 3.06 2607  82  10   8 0.00
Sat 08/29 20Z 1.73 2509  84   9   8 0.00
Sat 08/29 21Z 0.91 2410  85  10   8 0.00
Sat 08/29 22Z 0.73 2411  85  10   9 0.00
Sat 08/29 23Z 0.66 2414  81   9   9 0.00
Sun 08/30 00Z 0.81 2517  78   7   9 0.00
Sun 08/30 01Z 0.81 2518  74   6  10 0.00
Sun 08/30 02Z 0.85 2520  71  13  10 0.00
Sun 08/30 03Z 0.83 2622  65  25  11 0.00
Sun 08/30 04Z 0.65 2720  55  53  11 0.00
Sun 08/30 05Z 0.68 2722  61  61  12 0.00
Sun 08/30 06Z 0.79 2725  70  54  12 0.00
Sun 08/30 07Z 0.82 2725  75  68  12 0.00
Sun 08/30 08Z 0.92 2726  78  65  11 0.00
Sun 08/30 09Z 0.98 2727  79  54  11 0.00
Sun 08/30 10Z 0.97 2726  75  44  11 0.00
Sun 08/30 11Z 1.07 2727  73  40  11 0.00
Sun 08/30 12Z 1.02 2727  75  36  12 0.00
Sun 08/30 13Z 0.95 2725  75  64  12 0.00
Sun 08/30 14Z 0.92 2725  75  70  11 0.00
Sun 08/30 15Z 0.76 2720  78  64  11 0.00
Sun 08/30 16Z 0.72 2617  77  54  11 0.00
Sun 08/30 17Z 0.74 2516  78  45  12 0.00
Sun 08/30 18Z 0.75 2516  78  67  12 0.00
Sun 08/30 19Z 0.87 2416  81  76  12 0.00
Sun 08/30 20Z 0.86 2417  80  85  12 0.00
Sun 08/30 21Z 0.87 2318  86  98  12 0.01
Sun 08/30 22Z 0.99 2622  94  93  11 0.16
Sun 08/30 23Z 0.92 2823  89  79  11 0.04
Mon 08/31 00Z 0.90 2923  92  74  11 0.00
Mon 08/31 01Z 0.74 3023  95  74  11 0.01
Mon 08/31 02Z 0.57 3022  96  55  11 0.01
Mon 08/31 03Z 0.39 3222  90  58  11 0.01
Mon 08/31 04Z 0.23 3322  82  46  10 0.00
Mon 08/31 05Z 0.14 3320  78  37  10 0.01
Mon 08/31 06Z 0.10 3417  77  26  10 0.00
Mon 08/31 07Z 0.07 3414  79  16  10 0.00
Mon 08/31 08Z 0.07 3313  75   3  10 0.00
Mon 08/31 09Z 0.08 3313  67   4  10 0.00
Mon 08/31 10Z 0.06 3312  61   6  10 0.00
Mon 08/31 11Z 0.05 3310  52   7  10 0.00
Mon 08/31 12Z 0.06 3308  47   7  11 0.00
Mon 08/31 13Z 0.09 3209  44   7  11 0.00
Mon 08/31 14Z 0.08 3207  42   7  11 0.00
Mon 08/31 15Z 0.11 3106  46   8  11 0.00
Mon 08/31 16Z 0.13 3006  50   8  11 0.00
Mon 08/31 17Z 0.10 3004  52   7  11 0.00
Mon 08/31 18Z 0.25 2904  55   6  10 0.00
Mon 08/31 19Z 0.31 2804  52   6  11 0.00
Mon 08/31 20Z 0.19 2703  47   6  11 0.00
Mon 08/31 21Z 0.18 2703  45   4  11 0.00
Mon 08/31 22Z 0.14 2703  44   1  11 0.00
Mon 08/31 23Z 0.20 2604  48   1  11 0.00
Tue 09/01 00Z 0.23 2505  54   2  11 0.00
Tue 09/01 01Z 0.22 2505  61   4  11 0.00
Tue 09/01 02Z 0.15 2304  64   5  11 0.00
Tue 09/01 03Z 0.14 2104  68   6  11 0.00
Tue 09/01 04Z 0.18 2105  71   8  11 0.00
Tue 09/01 05Z 0.19 2206  74  10  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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