NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260825_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)
=== ===== === ==== ==== === === === ====
Tue 08/25 18Z 0.57 3007  95  74   9 0.00
Tue 08/25 19Z 0.47 2909  93  70  10 0.00
Tue 08/25 20Z 0.36 3008  87  70  10 0.00
Tue 08/25 21Z 0.32 3108  86  65  10 0.00
Tue 08/25 22Z 0.21 3108  88  73  10 0.00
Tue 08/25 23Z 0.19 3108  91  78  10 0.02
Wed 08/26 00Z 0.14 3209  90  71  10 0.02
Wed 08/26 01Z 0.14 3210  92  61  10 0.00
Wed 08/26 02Z 0.18 3211  93  59  10 0.00
Wed 08/26 03Z 0.18 3211  92  59  10 0.00
Wed 08/26 04Z 0.16 3210  90  58  10 0.00
Wed 08/26 05Z 0.16 3211  88  62  10 0.00
Wed 08/26 06Z 0.17 3211  89  64  10 0.00
Wed 08/26 07Z 0.18 3112  89  61  10 0.00
Wed 08/26 08Z 0.15 3211  89  49  10 0.01
Wed 08/26 09Z 0.14 3211  90  39  10 0.00
Wed 08/26 10Z 0.12 3210  90  33  10 0.00
Wed 08/26 11Z 0.08 3208  88  30  10 0.00
Wed 08/26 12Z 0.06 3307  87  30  10 0.00
Wed 08/26 13Z 0.07 3206  88  30  10 0.00
Wed 08/26 14Z 0.05 3205  89  28  10 0.00
Wed 08/26 15Z 0.03 3303  89  24  10 0.00
Wed 08/26 16Z 0.04 3101  90  23  10 0.00
Wed 08/26 17Z 0.10 2702  90  22  10 0.00
Wed 08/26 18Z 0.09 2602  88  20  11 0.00
Wed 08/26 19Z 0.07 2302  86  18  11 0.00
Wed 08/26 20Z 0.06 2102  86  16  11 0.00
Wed 08/26 21Z 0.07 2003  85  13  11 0.00
Wed 08/26 22Z 0.11 2005  84  11  11 0.00
Wed 08/26 23Z 0.11 2005  81   7  12 0.00
Thu 08/27 00Z 0.11 2006  77   9  12 0.00
Thu 08/27 01Z 0.12 2007  73  13  12 0.00
Thu 08/27 02Z 0.13 2008  68  15  12 0.00
Thu 08/27 03Z 0.18 2010  63  17  12 0.00
Thu 08/27 04Z 0.21 2110  59  15  12 0.00
Thu 08/27 05Z 0.28 2112  61  15  12 0.00
Thu 08/27 06Z 0.32 2114  70  14  12 0.00
Thu 08/27 07Z 0.34 2115  77  13  12 0.00
Thu 08/27 08Z 0.38 2216  80  13  12 0.00
Thu 08/27 09Z 0.40 2117  84  13  12 0.01
Thu 08/27 10Z 0.40 2118  86  15  12 0.01
Thu 08/27 11Z 0.40 2119  86  25  12 0.00
Thu 08/27 12Z 0.40 2120  87  12  12 0.00
Thu 08/27 13Z 0.43 2120  87  32  12 0.00
Thu 08/27 14Z 0.48 2120  96  40  12 0.00
Thu 08/27 15Z 0.54 2122  97  44  12 0.00
Thu 08/27 16Z 0.48 2021  98  37  12 0.00
Thu 08/27 17Z 0.47 1921  97  31  12 0.01
Thu 08/27 18Z 0.51 1920  97  50  12 0.01
Thu 08/27 19Z 0.50 1920  96  64  13 0.00
Thu 08/27 20Z 0.43 1922  96  80  14 0.01
Thu 08/27 21Z 0.45 1924  97  66  14 0.02
Thu 08/27 22Z 0.49 1925  97  68  14 0.01
Thu 08/27 23Z 0.59 2027  97  72  14 0.01
Fri 08/28 00Z 0.60 2029  97  68  14 0.01
Fri 08/28 01Z 0.53 2031  94  49  15 0.00
Fri 08/28 02Z 0.75 2137  97  42  15 0.01
Fri 08/28 03Z 0.73 2133  91  43  15 0.01
Fri 08/28 04Z 0.74 2231  94  52  14 0.02
Fri 08/28 05Z 0.76 2230  94  57  13 0.03

Run total areal avg QPF for the Central_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