NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260310_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)
=== ===== === ==== ==== === === === ====
Tue 03/10 00Z 0.83 2327  28  40   8 0.00
Tue 03/10 01Z 1.10 2331  28  43   8 0.00
Tue 03/10 02Z 1.11 2333  29  42   8 0.00
Tue 03/10 03Z 1.10 2433  31  39   8 0.00
Tue 03/10 04Z 1.12 2533  34  37   8 0.00
Tue 03/10 05Z 1.09 2634  37  42   9 0.00
Tue 03/10 06Z 1.01 2632  35  49   8 0.00
Tue 03/10 07Z 1.04 2731  34  51   8 0.00
Tue 03/10 08Z 1.05 2730  34  52   8 0.00
Tue 03/10 09Z 1.00 2727  38  51   8 0.00
Tue 03/10 10Z 0.89 2725  42  50   8 0.00
Tue 03/10 11Z 0.78 2722  46  52   8 0.00
Tue 03/10 12Z 0.66 2719  50  54   8 0.00
Tue 03/10 13Z 0.58 2616  52  55   8 0.00
Tue 03/10 14Z 0.56 2416  53  54   8 0.00
Tue 03/10 15Z 0.57 2317  54  45   8 0.00
Tue 03/10 16Z 0.63 2319  55  47   8 0.00
Tue 03/10 17Z 0.81 2220  56  42   7 0.00
Tue 03/10 18Z 1.14 2322  56  60   7 0.00
Tue 03/10 19Z 1.40 2322  61  42   7 0.00
Tue 03/10 20Z 1.43 2323  69  45   7 0.00
Tue 03/10 21Z 1.25 2423  80  44   8 0.00
Tue 03/10 22Z 0.95 2524  87  46   8 0.00
Tue 03/10 23Z 0.84 2524  93  47   8 0.02
Wed 03/11 00Z 0.63 2622  97  42   7 0.02
Wed 03/11 01Z 0.48 2819  98  39   7 0.02
Wed 03/11 02Z 0.31 2815  98  55   7 0.01
Wed 03/11 03Z 0.25 2914  98  71   7 0.01
Wed 03/11 04Z 0.20 2912  98  51   7 0.01
Wed 03/11 05Z 0.14 3009  98  59   7 0.01
Wed 03/11 06Z 0.06 3004  97  72   7 0.01
Wed 03/11 07Z 0.04 1701  97  71   7 0.00
Wed 03/11 08Z 0.03 1608  98  73   7 0.01
Wed 03/11 09Z 0.03 1615  98  70   8 0.01
Wed 03/11 10Z 0.03 1619  98  65   8 0.03
Wed 03/11 11Z 0.04 1625  98  60   8 0.03
Wed 03/11 12Z 0.06 1728  98  54   8 0.03
Wed 03/11 13Z 0.09 1730  98  52   9 0.03
Wed 03/11 14Z 0.09 1733  97  39   9 0.02
Wed 03/11 15Z 0.16 1836  97  73   9 0.03
Wed 03/11 16Z 0.19 1837  96  71   9 0.03
Wed 03/11 17Z 0.22 1939  97  75  10 0.03
Wed 03/11 18Z 0.24 1941  97  71  11 0.01
Wed 03/11 19Z 0.28 1942  93  84  11 0.02
Wed 03/11 20Z 0.33 2041  95  88  11 0.05
Wed 03/11 21Z 0.35 2041  93  95  12 0.01
Wed 03/11 22Z 0.44 2045  97  95  11 0.07
Wed 03/11 23Z 0.41 2045  94  93  11 0.06
Thu 03/12 00Z 0.51 2046  92  93  12 0.01
Thu 03/12 01Z 0.60 2145  92  81  12 0.01
Thu 03/12 02Z 0.68 2146  94  84  13 0.01
Thu 03/12 03Z 0.66 2144  92  91  13 0.02
Thu 03/12 04Z 0.91 2148  97  82  12 0.09
Thu 03/12 05Z 1.34 2345  97  80  10 0.04
Thu 03/12 06Z 1.21 2435  98  39   9 0.05
Thu 03/12 07Z 1.33 2433  98  53   7 0.06
Thu 03/12 08Z 1.31 2535  96  58   4 0.05
Thu 03/12 09Z 1.04 2436  91  72   3 0.01
Thu 03/12 10Z 1.23 2537  92  66  -1 0.01
Thu 03/12 11Z 1.49 2538  90  14  -5 0.01

Run total areal avg QPF for the Central_Greens is: 0.95 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