NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260820_1800
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)
=== ===== === ==== ==== === === === ====
Thu 08/20 18Z 0.95 2705  84  42  11 0.00
Thu 08/20 19Z 0.91 2806  85  46  11 0.01
Thu 08/20 20Z 0.49 2907  83  47  11 0.02
Thu 08/20 21Z 0.33 3008  79  43  11 0.03
Thu 08/20 22Z 0.19 3208  75  49  11 0.01
Thu 08/20 23Z 0.16 3307  73  54  11 0.00
Fri 08/21 00Z 0.13 3506  70  41  11 0.00
Fri 08/21 01Z 0.15 0008  67  30  11 0.00
Fri 08/21 02Z 0.13 0009  65  27  10 0.01
Fri 08/21 03Z 0.09 0009  63  26  10 0.01
Fri 08/21 04Z 0.08 0009  59  29  10 0.00
Fri 08/21 05Z 0.09 0109  57  28  10 0.00
Fri 08/21 06Z 0.12 0110  56  23  10 0.00
Fri 08/21 07Z 0.17 0210  56  27  10 0.00
Fri 08/21 08Z 0.19 0309  57  29  10 0.00
Fri 08/21 09Z 0.21 0409  58  29  10 0.00
Fri 08/21 10Z 0.24 0409  59  31  10 0.00
Fri 08/21 11Z 0.25 0509  60  32  10 0.00
Fri 08/21 12Z 0.24 0508  61  31  10 0.00
Fri 08/21 13Z 0.26 0508  63  25  10 0.00
Fri 08/21 14Z 0.29 0608  67  22   9 0.00
Fri 08/21 15Z 0.44 0507  71  19   9 0.00
Fri 08/21 16Z 1.03 0506  73  15   9 0.00
Fri 08/21 17Z 1.55 0505  74  12   9 0.00
Fri 08/21 18Z 1.59 0604  74  10   9 0.00
Fri 08/21 19Z 1.35 0503  74   8  10 0.00
Fri 08/21 20Z 1.03 0602  75   7  10 0.00
Fri 08/21 21Z 0.69 0603  75   6  10 0.00
Fri 08/21 22Z 0.37 0603  76   5  10 0.00
Fri 08/21 23Z 0.33 0603  76   5  10 0.00
Sat 08/22 00Z 0.41 0705  77   8  10 0.00
Sat 08/22 01Z 0.50 0807  78   9  10 0.00
Sat 08/22 02Z 0.46 0908  78  11  10 0.00
Sat 08/22 03Z 0.37 1007  78  14  10 0.00
Sat 08/22 04Z 0.35 1108  78  14  10 0.00
Sat 08/22 05Z 0.37 1109  77  16  10 0.00
Sat 08/22 06Z 0.34 1109  77  19  10 0.00
Sat 08/22 07Z 0.34 1109  78  23  10 0.00
Sat 08/22 08Z 0.34 1110  79  23  10 0.00
Sat 08/22 09Z 0.34 1110  78  26  10 0.00
Sat 08/22 10Z 0.36 1112  78  31  10 0.00
Sat 08/22 11Z 0.37 1113  80  37  10 0.00
Sat 08/22 12Z 0.39 1215  80  42  10 0.00
Sat 08/22 13Z 0.36 1214  82  45  11 0.00
Sat 08/22 14Z 0.34 1213  85  45  11 0.00
Sat 08/22 15Z 0.32 1212  87  49  11 0.01
Sat 08/22 16Z 0.36 1211  90  55  11 0.01
Sat 08/22 17Z 0.67 1211  93  54  11 0.01
Sat 08/22 18Z 0.63 1210  94  50  11 0.01
Sat 08/22 19Z 0.36 1211  95  42  11 0.01
Sat 08/22 20Z 0.31 1211  95  38  11 0.01
Sat 08/22 21Z 0.30 1212  95  31  12 0.00
Sat 08/22 22Z 0.30 1212  95  29  12 0.00
Sat 08/22 23Z 0.28 1212  95  34  12 0.01
Sun 08/23 00Z 0.28 1313  95  35  12 0.01
Sun 08/23 01Z 0.31 1214  95  35  12 0.01
Sun 08/23 02Z 0.30 1314  94  33  13 0.01
Sun 08/23 03Z 0.27 1313  94  29  13 0.01
Sun 08/23 04Z 0.23 1312  94  33  13 0.01
Sun 08/23 05Z 0.20 1411  94  43  13 0.01

Run total areal avg QPF for the greens is: 0.22 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