NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260907_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 09/07 12Z 0.19 3421  82  20   8 0.00
Mon 09/07 13Z 0.22 3422  79  15   8 0.00
Mon 09/07 14Z 0.21 3425  75  11   8 0.00
Mon 09/07 15Z 0.20 3424  70   9   9 0.00
Mon 09/07 16Z 0.21 3422  67   7   9 0.00
Mon 09/07 17Z 0.29 3419  67   5   9 0.00
Mon 09/07 18Z 0.55 3319  68   4   9 0.00
Mon 09/07 19Z 1.24 3318  68   4   9 0.00
Mon 09/07 20Z 2.41 3316  68   6   9 0.00
Mon 09/07 21Z 2.10 3217  69   8   9 0.00
Mon 09/07 22Z 1.09 3116  71  12   9 0.00
Mon 09/07 23Z 1.67 3118  72  14   9 0.00
Tue 09/08 00Z 1.53 3118  73  21   9 0.00
Tue 09/08 01Z 1.54 3119  75  26   9 0.00
Tue 09/08 02Z 1.04 3119  76  36   9 0.00
Tue 09/08 03Z 0.68 3216  76  52   9 0.00
Tue 09/08 04Z 0.52 3215  74  60  10 0.00
Tue 09/08 05Z 0.54 3115  74  67  10 0.00
Tue 09/08 06Z 0.65 3118  76  71   9 0.00
Tue 09/08 07Z 0.63 3117  75  60  10 0.00
Tue 09/08 08Z 0.65 3017  75  59  10 0.00
Tue 09/08 09Z 0.64 3017  75  61  10 0.00
Tue 09/08 10Z 0.67 3019  77  65   9 0.00
Tue 09/08 11Z 0.60 3118  78  71   9 0.00
Tue 09/08 12Z 0.46 3116  81  77   9 0.01
Tue 09/08 13Z 0.36 3115  83  84   9 0.01
Tue 09/08 14Z 0.31 3113  84  88  10 0.01
Tue 09/08 15Z 0.32 3113  87  83   9 0.01
Tue 09/08 16Z 0.29 3213  90  59   9 0.01
Tue 09/08 17Z 0.22 3312  89  42   9 0.00
Tue 09/08 18Z 0.15 3311  87  37  10 0.00
Tue 09/08 19Z 0.15 3309  81  35  10 0.00
Tue 09/08 20Z 0.14 3309  77  53  10 0.00
Tue 09/08 21Z 0.11 3307  72  64  10 0.00
Tue 09/08 22Z 0.11 3307  66  66  11 0.00
Tue 09/08 23Z 0.10 3205  62  62  11 0.00
Wed 09/09 00Z 0.12 3004  60  61  11 0.00
Wed 09/09 01Z 0.13 3004  63  64  11 0.00
Wed 09/09 02Z 0.16 2804  67  69  11 0.00
Wed 09/09 03Z 0.20 2605  73  73  11 0.00
Wed 09/09 04Z 0.21 2506  80  75  11 0.00
Wed 09/09 05Z 0.21 2307  87  72  11 0.00
Wed 09/09 06Z 0.22 2209  92  66  11 0.00
Wed 09/09 07Z 0.22 2111  93  60  11 0.00
Wed 09/09 08Z 0.29 2213  94  58  11 0.00
Wed 09/09 09Z 0.32 2215  94  60  11 0.00
Wed 09/09 10Z 0.29 2115  90  56  12 0.00
Wed 09/09 11Z 0.34 2118  89  63  12 0.00
Wed 09/09 12Z 0.40 2120  88  58  12 0.00
Wed 09/09 13Z 0.43 2221  87  52  11 0.00
Wed 09/09 14Z 0.43 2220  85  55  11 0.00
Wed 09/09 15Z 0.43 2121  82  45  12 0.00
Wed 09/09 16Z 0.46 2120  86  24  12 0.00
Wed 09/09 17Z 0.46 2121  86  11  12 0.00
Wed 09/09 18Z 0.44 2122  86  41  12 0.00
Wed 09/09 19Z 0.47 2124  88  58  12 0.00
Wed 09/09 20Z 0.48 2127  93  74  13 0.01
Wed 09/09 21Z 0.59 2129  93  73  13 0.02
Wed 09/09 22Z 0.70 2232  94  66  14 0.01
Wed 09/09 23Z 0.73 2233  93  57  14 0.03

Run total areal avg QPF for the greens is: 0.12 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