NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260201_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)
=== ===== === ==== ==== === === === ====
Sun 02/01 18Z 0.06 0013  79  11 -11 0.00
Sun 02/01 19Z 0.06 3516  78  11 -10 0.00
Sun 02/01 20Z 0.07 0019  76  11 -10 0.00
Sun 02/01 21Z 0.09 0021  70  11  -9 0.00
Sun 02/01 22Z 0.10 0025  64  11  -9 0.00
Sun 02/01 23Z 0.10 0027  57  10  -9 0.00
Mon 02/02 00Z 0.09 0028  55  10  -9 0.00
Mon 02/02 01Z 0.10 0029  54  10  -9 0.00
Mon 02/02 02Z 0.09 0029  53  11 -10 0.00
Mon 02/02 03Z 0.06 3527  53  12 -10 0.00
Mon 02/02 04Z 0.03 3525  53  15  -9 0.00
Mon 02/02 05Z 0.02 3425  52  21  -9 0.00
Mon 02/02 06Z 0.02 3524  48  29  -9 0.00
Mon 02/02 07Z 0.02 3525  43  34  -9 0.00
Mon 02/02 08Z 0.02 3525  42  35  -9 0.00
Mon 02/02 10Z 0.02 3525  39  33  -8 0.00
Mon 02/02 11Z 0.02 3525  37  30  -8 0.00
Mon 02/02 12Z 0.02 3425  38  31  -8 0.00
Mon 02/02 13Z 0.02 3425  37  32  -8 0.00
Mon 02/02 14Z 0.02 3525  37  29  -8 0.00
Mon 02/02 15Z 0.02 3423  38  27  -8 0.00
Mon 02/02 16Z 0.03 3422  39  24  -8 0.00
Mon 02/02 17Z 0.05 3421  36  19  -9 0.00
Mon 02/02 18Z 0.09 3322  38  16  -9 0.00
Mon 02/02 19Z 0.10 3323  41  14  -9 0.00
Mon 02/02 20Z 0.09 3323  39  12  -9 0.00
Mon 02/02 21Z 0.09 3322  38  10  -9 0.00
Mon 02/02 22Z 0.09 3322  37   9  -9 0.00
Mon 02/02 23Z 0.10 3321  37   9  -9 0.00
Tue 02/03 00Z 0.10 3319  37  11  -9 0.00
Tue 02/03 01Z 0.08 3318  34  22  -8 0.00
Tue 02/03 02Z 0.06 3417  33  40  -8 0.00
Tue 02/03 03Z 0.07 3316  38  48  -9 0.00
Tue 02/03 04Z 0.05 3314  39  49  -9 0.00
Tue 02/03 05Z 0.07 3313  41  48  -9 0.00
Tue 02/03 06Z 0.08 3313  42  48  -9 0.00
Tue 02/03 07Z 0.09 3212  42  48  -9 0.00
Tue 02/03 08Z 0.11 3212  42  48  -9 0.00
Tue 02/03 09Z 0.11 3210  42  57  -9 0.00
Tue 02/03 10Z 0.13 3109  41  56  -9 0.00
Tue 02/03 11Z 0.12 3007  41  44  -9 0.00
Tue 02/03 12Z 0.10 3006  40  24  -9 0.00
Tue 02/03 13Z 0.09 2904  39  16  -9 0.00
Tue 02/03 14Z 0.11 2604  39  13  -9 0.00
Tue 02/03 15Z 0.13 2405  40  16  -9 0.00
Tue 02/03 16Z 0.18 2307  42  29  -9 0.00
Tue 02/03 17Z 0.22 2308  42  82 -10 0.00
Tue 02/03 18Z 0.26 2308  40  89 -10 0.00
Tue 02/03 19Z 0.30 2208  48  73 -10 0.00
Tue 02/03 20Z 0.34 2308  65  51 -11 0.00
Tue 02/03 21Z 0.35 2309  80  31 -11 0.00
Tue 02/03 22Z 0.34 2509  86  26 -11 0.00
Tue 02/03 23Z 0.34 2510  91  30 -12 0.00
Wed 02/04 00Z 0.43 2512  94  36 -12 0.00
Wed 02/04 01Z 0.50 2513  93  60 -12 0.00
Wed 02/04 02Z 0.50 2614  91  75 -12 0.00
Wed 02/04 03Z 0.51 2614  86  80 -12 0.00
Wed 02/04 04Z 0.59 2716  92  82 -13 0.00
Wed 02/04 05Z 0.60 2715  94  77 -13 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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