NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260211_1200
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)
=== ===== === ==== ==== === === === ====
Wed 02/11 12Z 0.51 2918  95  75  -9 0.00
Wed 02/11 13Z 0.64 2921  97  83 -10 0.00
Wed 02/11 14Z 0.74 2920  96  80 -10 0.00
Wed 02/11 15Z 0.94 2918  94  76 -10 0.00
Wed 02/11 16Z 1.12 2918  94  78  -9 0.00
Wed 02/11 17Z 1.30 2816  96  83  -9 0.00
Wed 02/11 18Z 1.06 2716  97  84  -9 0.01
Wed 02/11 19Z 1.21 2818  97  85  -9 0.01
Wed 02/11 20Z 1.21 2819  96  84  -9 0.02
Wed 02/11 21Z 1.45 2921  94  84  -9 0.02
Wed 02/11 22Z 1.02 3022  94  82 -10 0.02
Wed 02/11 23Z 0.80 3123  95  85 -11 0.03
Thu 02/12 00Z 0.75 3224  94  85 -13 0.02
Thu 02/12 02Z 0.33 3325  95  84 -13 0.01
Thu 02/12 03Z 0.31 3326  95  82 -13 0.01
Thu 02/12 04Z 0.32 3325  95  82 -13 0.01
Thu 02/12 05Z 0.31 3325  94  81 -13 0.01
Thu 02/12 06Z 0.31 3325  94  79 -13 0.01
Thu 02/12 07Z 0.24 3326  93  77 -13 0.01
Thu 02/12 08Z 0.15 3426  93  77 -13 0.00
Thu 02/12 09Z 0.13 3426  93  77 -12 0.00
Thu 02/12 10Z 0.13 3425  94  76 -12 0.00
Thu 02/12 11Z 0.12 3424  94  76 -12 0.00
Thu 02/12 12Z 0.10 3424  93  74 -12 0.00
Thu 02/12 13Z 0.10 3424  92  68 -12 0.00
Thu 02/12 14Z 0.12 3324  92  64 -12 0.00
Thu 02/12 15Z 0.13 3323  92  62 -11 0.00
Thu 02/12 16Z 0.13 3323  91  62 -11 0.00
Thu 02/12 17Z 0.17 3323  91  55 -12 0.00
Thu 02/12 18Z 0.22 3322  92  39 -12 0.00
Thu 02/12 19Z 0.26 3222  91  18 -12 0.00
Thu 02/12 20Z 0.27 3222  89   8 -12 0.00
Thu 02/12 21Z 0.24 3322  82   6 -12 0.00
Thu 02/12 22Z 0.15 3323  70  11 -11 0.00
Thu 02/12 23Z 0.08 3424  61  10 -10 0.00
Fri 02/13 00Z 0.04 3424  61  13 -10 0.00
Fri 02/13 01Z 0.04 3524  59  15  -9 0.00
Fri 02/13 02Z 0.04 3524  58  16  -9 0.00
Fri 02/13 03Z 0.04 3523  61  17  -9 0.00
Fri 02/13 04Z 0.03 3522  63  18  -9 0.00
Fri 02/13 05Z 0.02 3421  64  21  -9 0.00
Fri 02/13 06Z 0.03 3420  64  23  -9 0.00
Fri 02/13 07Z 0.06 3420  63  27  -9 0.00
Fri 02/13 08Z 0.07 3320  64  28  -9 0.00
Fri 02/13 09Z 0.09 3320  63  24  -9 0.00
Fri 02/13 10Z 0.13 3320  63  22  -9 0.00
Fri 02/13 11Z 0.16 3220  62  20  -9 0.00
Fri 02/13 12Z 0.18 3221  62  21  -9 0.00
Fri 02/13 13Z 0.22 3121  64  20 -10 0.00
Fri 02/13 14Z 0.23 3120  61  19 -10 0.00
Fri 02/13 15Z 0.25 3119  58  19 -10 0.00
Fri 02/13 16Z 0.28 3018  57  23 -10 0.00
Fri 02/13 17Z 0.32 3017  55  25 -10 0.00
Fri 02/13 18Z 0.36 2917  55  31 -10 0.00
Fri 02/13 19Z 0.40 2917  61  51 -10 0.00
Fri 02/13 20Z 0.48 2817  70  66 -11 0.00
Fri 02/13 21Z 0.55 2818  72  47 -11 0.00
Fri 02/13 22Z 0.57 2719  71  42 -10 0.00
Fri 02/13 23Z 0.52 2720  68  43 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.19 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