NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261001_0600
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)
=== ===== === ==== ==== === === === ====
Thu 10/01 06Z 0.42 2813  90  76  10 0.00
Thu 10/01 07Z 0.46 2813  88  62  10 0.00
Thu 10/01 08Z 0.37 2711  90  54  10 0.00
Thu 10/01 09Z 0.40 2711  89  40  10 0.00
Thu 10/01 10Z 0.34 2509  89  47  10 0.00
Thu 10/01 11Z 0.30 2308  89  56  10 0.00
Thu 10/01 12Z 0.32 2211  90  75  10 0.00
Thu 10/01 13Z 0.38 2215  91  92  10 0.00
Thu 10/01 14Z 0.41 2117  93  93  11 0.00
Thu 10/01 15Z 0.50 2219  96  95  11 0.01
Thu 10/01 16Z 0.58 2222  96  94  11 0.01
Thu 10/01 17Z 0.65 2322  94  92  11 0.01
Thu 10/01 18Z 0.68 2323  90  83  12 0.00
Thu 10/01 19Z 0.72 2324  94  93  13 0.00
Thu 10/01 20Z 0.66 2324  96  94  13 0.01
Thu 10/01 21Z 0.71 2327  97  83  14 0.03
Thu 10/01 22Z 0.80 2528  96  63  14 0.02
Thu 10/01 23Z 0.82 2529  96  58  14 0.02
Fri 10/02 00Z 0.88 2630  95  80  14 0.02
Fri 10/02 01Z 0.80 2629  92  83  15 0.01
Fri 10/02 02Z 0.78 2628  91  85  15 0.01
Fri 10/02 03Z 0.82 2528  92  84  14 0.01
Fri 10/02 04Z 0.87 2430  92  72  14 0.01
Fri 10/02 05Z 0.84 2432  89  66  15 0.00
Fri 10/02 06Z 0.91 2336  88  62  15 0.00
Fri 10/02 07Z 0.97 2440  82  74  16 0.00
Fri 10/02 08Z 1.05 2442  77  82  16 0.01
Fri 10/02 09Z 1.07 2441  84  65  15 0.01
Fri 10/02 10Z 1.11 2440  93  76  15 0.01
Fri 10/02 11Z 1.14 2441  94  93  15 0.02
Fri 10/02 12Z 1.09 2537  96  94  14 0.04
Fri 10/02 13Z 1.13 2535  97  94  14 0.06
Fri 10/02 14Z 0.97 2729  97  92  13 0.09
Fri 10/02 15Z 0.61 2921  97  72  13 0.04
Fri 10/02 16Z 0.54 2920  96  54  12 0.02
Fri 10/02 17Z 0.44 2919  95  66  12 0.02
Fri 10/02 18Z 0.44 2922  94  54  11 0.01
Fri 10/02 19Z 0.42 2921  90  72  10 0.01
Fri 10/02 20Z 0.40 2921  84  56  10 0.00
Fri 10/02 21Z 0.40 3021  82  38   9 0.00
Fri 10/02 22Z 0.36 3021  76  15   8 0.00
Fri 10/02 23Z 0.32 3122  75   6   7 0.00
Sat 10/03 00Z 0.31 3222  75   5   6 0.00
Sat 10/03 01Z 0.37 3225  79   3   5 0.00
Sat 10/03 02Z 0.39 3225  80   1   5 0.00
Sat 10/03 03Z 0.42 3226  78   2   4 0.00
Sat 10/03 04Z 0.36 3225  78   6   4 0.00
Sat 10/03 05Z 0.40 3225  79  11   4 0.00
Sat 10/03 06Z 0.34 3324  81   9   3 0.00
Sat 10/03 07Z 0.28 3322  78   5   3 0.00
Sat 10/03 08Z 0.23 3320  78   4   3 0.00
Sat 10/03 09Z 0.28 3220  81   4   2 0.00
Sat 10/03 10Z 0.28 3220  82   3   2 0.00
Sat 10/03 11Z 0.18 3319  76   2   3 0.00
Sat 10/03 12Z 0.18 3318  74   2   3 0.00
Sat 10/03 13Z 0.18 3217  72   2   3 0.00
Sat 10/03 14Z 0.17 3216  66   2   3 0.00
Sat 10/03 15Z 0.18 3216  63   2   3 0.00
Sat 10/03 16Z 0.16 3215  58   2   3 0.00
Sat 10/03 17Z 0.15 3313  57   3   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.51 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