Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260627_0600
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)
=== ===== === ==== ==== === === === ====
Sat 06/27 06Z 0.23 3009  84  64  11 0.00
Sat 06/27 07Z 0.22 3109  84  64  11 0.00
Sat 06/27 08Z 0.20 3109  84  65  11 0.00
Sat 06/27 09Z 0.17 3108  84  67  11 0.00
Sat 06/27 10Z 0.15 3106  84  70  11 0.00
Sat 06/27 11Z 0.15 3006  85  74  11 0.00
Sat 06/27 12Z 0.13 3005  86  76  11 0.00
Sat 06/27 13Z 0.12 3005  86  75  11 0.00
Sat 06/27 14Z 0.10 3104  85  70  11 0.00
Sat 06/27 15Z 0.09 3003  86  67  11 0.00
Sat 06/27 16Z 0.08 3002  87  65  11 0.00
Sat 06/27 17Z 0.08 3102  87  60  11 0.01
Sat 06/27 18Z 0.08 3102  86  57  11 0.02
Sat 06/27 19Z 0.08 3202  85  51  11 0.02
Sat 06/27 20Z 0.12 3203  85  49  12 0.02
Sat 06/27 21Z 0.10 3303  84  47  12 0.03
Sat 06/27 22Z 0.07 3403  84  47  12 0.01
Sat 06/27 23Z 0.06 3503  83  52  12 0.01
Sun 06/28 00Z 0.06 0002  82  49  12 0.01
Sun 06/28 01Z 0.08 0102  81  48  12 0.00
Sun 06/28 02Z 0.10 0102  79  48  12 0.00
Sun 06/28 03Z 0.08 0002  79  51  11 0.00
Sun 06/28 04Z 0.06 0002  80  53  11 0.00
Sun 06/28 05Z 0.07 0003  79  54  11 0.00
Sun 06/28 06Z 0.06 3503  78  55  11 0.00
Sun 06/28 07Z 0.06 3404  76  53  11 0.00
Sun 06/28 08Z 0.07 3405  73  45  11 0.00
Sun 06/28 09Z 0.05 3406  71  35  11 0.00
Sun 06/28 10Z 0.04 3507  70  27  11 0.00
Sun 06/28 11Z 0.02 3507  69  25  11 0.00
Sun 06/28 12Z 0.03 0007  70  24  11 0.00
Sun 06/28 13Z 0.05 0107  71  24  11 0.00
Sun 06/28 14Z 0.08 0206  71  25  11 0.00
Sun 06/28 15Z 0.10 0305  73  24  11 0.00
Sun 06/28 16Z 0.11 0204  75  23  11 0.00
Sun 06/28 17Z 0.08 0104  77  21  11 0.00
Sun 06/28 18Z 0.08 0004  79  19  11 0.00
Sun 06/28 19Z 0.09 3504  80  18  12 0.00
Sun 06/28 20Z 0.11 3404  80  15  12 0.00
Sun 06/28 21Z 0.11 3404  80  10  12 0.00
Sun 06/28 22Z 0.09 3405  79   9  12 0.00
Sun 06/28 23Z 0.07 3406  77   9  12 0.00
Mon 06/29 00Z 0.05 0008  76  10  12 0.00
Mon 06/29 01Z 0.07 0009  77  12  12 0.00
Mon 06/29 02Z 0.12 0109  75  11  12 0.00
Mon 06/29 03Z 0.13 0208  74  11  12 0.00
Mon 06/29 04Z 0.17 0308  72  13  12 0.00
Mon 06/29 05Z 0.15 0306  71  15  12 0.00
Mon 06/29 06Z 0.06 0204  69  17  12 0.00
Mon 06/29 07Z 0.02 0004  67  18  12 0.00
Mon 06/29 08Z 0.04 3405  67  20  12 0.00
Mon 06/29 09Z 0.05 3407  66  22  12 0.00
Mon 06/29 10Z 0.03 3508  64  23  12 0.00
Mon 06/29 11Z 0.04 0008  63  21  12 0.00
Mon 06/29 12Z 0.06 0108  63  20  12 0.00
Mon 06/29 13Z 0.08 0107  63  19  12 0.00
Mon 06/29 14Z 0.06 0105  66  21  12 0.00
Mon 06/29 15Z 0.08 0104  71  21  12 0.00
Mon 06/29 16Z 0.08 0002  73  21  12 0.00
Mon 06/29 17Z 0.13 0300  72  21  12 0.01

Run total areal avg QPF for the greens is: 0.14 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