NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260812_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 08/12 12Z 0.22 3213  81  72  11 0.00
Wed 08/12 13Z 0.20 3313  80  73  11 0.00
Wed 08/12 14Z 0.28 3210  80  76  11 0.00
Wed 08/12 15Z 1.08 3107  79  76  11 0.00
Wed 08/12 16Z 1.66 3006  76  77  12 0.00
Wed 08/12 17Z 1.57 2904  72  81  12 0.00
Wed 08/12 18Z 1.23 2603  70  86  13 0.00
Wed 08/12 19Z 0.92 2506  78  93  12 0.07
Wed 08/12 20Z 0.43 2410  88  95  12 0.16
Wed 08/12 21Z 0.35 2508  83  87  12 0.06
Wed 08/12 22Z 0.33 2709  87  81  12 0.04
Wed 08/12 23Z 0.36 2710  83  78  12 0.00
Thu 08/13 00Z 0.36 2810  83  87  12 0.02
Thu 08/13 01Z 0.37 2911  87  87  12 0.03
Thu 08/13 02Z 0.24 3008  82  85  12 0.00
Thu 08/13 03Z 0.28 2706  82  89  12 0.00
Thu 08/13 04Z 0.24 2405  83  88  12 0.00
Thu 08/13 05Z 0.36 2408  85  95  12 0.00
Thu 08/13 06Z 0.43 2411  90  96  11 0.03
Thu 08/13 07Z 0.52 2513  94  89  11 0.07
Thu 08/13 08Z 0.56 2515  97  88  11 0.04
Thu 08/13 09Z 0.59 2616  96  68  11 0.05
Thu 08/13 10Z 0.57 2616  97  55  11 0.01
Thu 08/13 11Z 0.57 2716  97  57  11 0.02
Thu 08/13 12Z 0.47 2915  96  56  11 0.01
Thu 08/13 13Z 0.39 3015  95  54  11 0.00
Thu 08/13 14Z 0.38 3013  95  57  11 0.00
Thu 08/13 15Z 0.37 3113  96  60  11 0.00
Thu 08/13 16Z 0.44 3014  94  63  11 0.00
Thu 08/13 17Z 0.53 3013  94  63  11 0.01
Thu 08/13 18Z 0.58 3014  93  65  11 0.02
Thu 08/13 19Z 1.02 3015  91  61  11 0.04
Thu 08/13 20Z 1.20 3015  91  55  11 0.01
Thu 08/13 21Z 2.03 3018  89  45  11 0.01
Thu 08/13 22Z 2.34 3020  87  33  11 0.00
Thu 08/13 23Z 1.12 3021  87  38  11 0.00
Fri 08/14 00Z 0.78 3122  84  44  11 0.00
Fri 08/14 01Z 0.59 3224  85  38  10 0.03
Fri 08/14 02Z 0.44 3225  88  37  10 0.00
Fri 08/14 03Z 0.41 3226  87  24   9 0.01
Fri 08/14 04Z 0.35 3226  85  24   9 0.00
Fri 08/14 05Z 0.30 3224  86  19   9 0.00
Fri 08/14 06Z 0.26 3223  83  17   8 0.00
Fri 08/14 07Z 0.25 3222  79  16   8 0.00
Fri 08/14 08Z 0.29 3222  78  16   8 0.00
Fri 08/14 09Z 0.32 3224  77  15   8 0.00
Fri 08/14 10Z 0.32 3225  69  15   8 0.00
Fri 08/14 11Z 0.32 3226  67  14   8 0.00
Fri 08/14 12Z 0.29 3225  65  13   8 0.00
Fri 08/14 13Z 0.27 3224  65  15   9 0.00
Fri 08/14 14Z 0.21 3222  63  18   9 0.00
Fri 08/14 15Z 0.22 3221  63  20   9 0.00
Fri 08/14 16Z 0.22 3221  61  23   9 0.00
Fri 08/14 17Z 0.27 3222  63  25   9 0.00
Fri 08/14 18Z 0.33 3221  64  27   9 0.00
Fri 08/14 19Z 0.48 3121  65  31   8 0.00
Fri 08/14 20Z 0.70 3120  64  36   8 0.00
Fri 08/14 21Z 0.66 3118  63  35   9 0.00
Fri 08/14 22Z 0.66 3119  62  32   9 0.00
Fri 08/14 23Z 0.59 3119  60  26   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.74 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