Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260628_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)
=== ===== === ==== ==== === === === ====
Sun 06/28 06Z 0.04 3001  76  72  12 0.00
Sun 06/28 07Z 0.04 3203  75  69  12 0.00
Sun 06/28 08Z 0.05 3303  74  64  12 0.00
Sun 06/28 09Z 0.04 3404  73  58  12 0.00
Sun 06/28 10Z 0.04 3405  72  53  12 0.00
Sun 06/28 11Z 0.04 3506  71  49  13 0.00
Sun 06/28 12Z 0.06 0007  68  45  13 0.00
Sun 06/28 13Z 0.08 0008  68  45  13 0.00
Sun 06/28 14Z 0.14 0007  71  52  12 0.00
Sun 06/28 15Z 0.34 0006  74  57  12 0.00
Sun 06/28 16Z 0.82 0105  74  56  12 0.00
Sun 06/28 17Z 0.77 0005  71  49  12 0.03
Sun 06/28 18Z 0.55 0006  70  40  13 0.01
Sun 06/28 19Z 0.39 3505  68  29  13 0.01
Sun 06/28 20Z 0.26 3505  70  29  13 0.00
Sun 06/28 21Z 0.35 3305  71  35  13 0.00
Sun 06/28 22Z 0.22 3306  71  37  13 0.00
Sun 06/28 23Z 0.11 3307  67  39  13 0.00
Mon 06/29 00Z 0.05 3409  61  40  13 0.00
Mon 06/29 01Z 0.09 3511  58  45  13 0.00
Mon 06/29 02Z 0.20 0012  53  46  13 0.00
Mon 06/29 03Z 0.24 0112  51  43  13 0.00
Mon 06/29 04Z 0.20 0111  52  44  13 0.00
Mon 06/29 05Z 0.17 0109  58  45  13 0.00
Mon 06/29 06Z 0.12 0008  64  42  12 0.00
Mon 06/29 07Z 0.09 3508  68  37  12 0.00
Mon 06/29 08Z 0.07 3509  72  26  12 0.00
Mon 06/29 09Z 0.06 3409  73  14  12 0.00
Mon 06/29 10Z 0.06 3410  71   9  12 0.00
Mon 06/29 11Z 0.03 3510  69   5  12 0.00
Mon 06/29 12Z 0.08 3509  66   5  12 0.00
Mon 06/29 13Z 0.06 3508  67   6  12 0.00
Mon 06/29 14Z 0.10 3507  69  10  12 0.00
Mon 06/29 15Z 0.26 3505  70  15  12 0.00
Mon 06/29 16Z 0.27 3404  71  18  12 0.00
Mon 06/29 17Z 0.51 3304  71  22  12 0.00
Mon 06/29 18Z 0.84 3104  69  25  12 0.00
Mon 06/29 19Z 0.70 3204  65  22  13 0.00
Mon 06/29 20Z 0.77 3105  60  20  13 0.00
Mon 06/29 21Z 0.49 3204  57  17  13 0.00
Mon 06/29 22Z 0.24 3103  54  14  14 0.00
Mon 06/29 23Z 0.12 3102  55  10  14 0.00
Tue 06/30 00Z 0.13 2902  57   7  14 0.00
Tue 06/30 01Z 0.21 2602  60   5  13 0.00
Tue 06/30 02Z 0.25 2503  62   4  13 0.00
Tue 06/30 03Z 0.34 2404  65   4  13 0.00
Tue 06/30 04Z 0.50 2406  67   7  13 0.00
Tue 06/30 05Z 0.60 2408  67   7  13 0.00
Tue 06/30 06Z 0.68 2510  70   7  13 0.00
Tue 06/30 07Z 0.71 2511  73  10  13 0.00
Tue 06/30 08Z 0.70 2512  74  14  13 0.00
Tue 06/30 09Z 0.81 2513  77  18  12 0.00
Tue 06/30 10Z 0.91 2514  74  22  12 0.00
Tue 06/30 11Z 0.91 2517  73  26  12 0.00
Tue 06/30 12Z 0.76 2516  77  26  13 0.00
Tue 06/30 13Z 0.79 2517  77  30  13 0.00
Tue 06/30 14Z 0.83 2617  82  34  13 0.00
Tue 06/30 15Z 0.77 2514  81  36  13 0.00
Tue 06/30 16Z 1.28 2510  82  37  13 0.00
Tue 06/30 17Z 1.45 2309  80  59  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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