NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260831_0000
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)
=== ===== === ==== ==== === === === ====
Mon 08/31 00Z 0.67 2819  91  93  11 0.00
Mon 08/31 01Z 0.69 2921  93  83  10 0.00
Mon 08/31 02Z 0.51 3120  97  77  10 0.01
Mon 08/31 03Z 0.33 3219  92  58  10 0.00
Mon 08/31 04Z 0.21 3318  87  25  10 0.00
Mon 08/31 05Z 0.13 3316  83   7  10 0.00
Mon 08/31 06Z 0.09 3314  80   6  10 0.00
Mon 08/31 07Z 0.07 3412  78   2  10 0.00
Mon 08/31 08Z 0.06 3410  78   1  10 0.00
Mon 08/31 09Z 0.06 3410  80   1  10 0.00
Mon 08/31 10Z 0.05 3309  80   1  10 0.00
Mon 08/31 11Z 0.06 3308  77   1  10 0.00
Mon 08/31 12Z 0.08 3308  74   1  10 0.00
Mon 08/31 13Z 0.08 3207  72   2  10 0.00
Mon 08/31 14Z 0.09 3206  70   2  10 0.00
Mon 08/31 15Z 0.09 3104  70   3  10 0.00
Mon 08/31 16Z 0.13 2803  73   7  10 0.00
Mon 08/31 17Z 0.34 2503  75  12  10 0.00
Mon 08/31 18Z 0.59 2504  73  19  10 0.00
Mon 08/31 19Z 0.92 2505  72  29  11 0.00
Mon 08/31 20Z 0.50 2504  72  34  11 0.00
Mon 08/31 21Z 0.37 2404  73  34  11 0.00
Mon 08/31 22Z 0.26 2404  76  40  11 0.00
Mon 08/31 23Z 0.20 2304  76  40  11 0.00
Tue 09/01 00Z 0.24 2305  79  45  11 0.00
Tue 09/01 01Z 0.21 2304  82  50  11 0.00
Tue 09/01 02Z 0.19 2204  84  49  11 0.00
Tue 09/01 03Z 0.17 2304  87  50  11 0.00
Tue 09/01 04Z 0.12 2203  89  52  11 0.00
Tue 09/01 05Z 0.09 2103  91  55  11 0.00
Tue 09/01 06Z 0.03 1703  93  67  11 0.00
Tue 09/01 07Z 0.05 1504  95  83  11 0.00
Tue 09/01 08Z 0.08 1406  96  88  11 0.02
Tue 09/01 09Z 0.09 1406  97  83  11 0.01
Tue 09/01 10Z 0.09 1408  97  74  11 0.01
Tue 09/01 11Z 0.07 1509  98  74  12 0.01
Tue 09/01 12Z 0.10 1511  98  75  12 0.02
Tue 09/01 13Z 0.11 1412  98  80  12 0.01
Tue 09/01 14Z 0.10 1512  97  85  12 0.01
Tue 09/01 15Z 0.09 1513  97  92  12 0.01
Tue 09/01 16Z 0.11 1514  97  95  12 0.01
Tue 09/01 17Z 0.14 1413  96  97  12 0.01
Tue 09/01 18Z 0.17 1413  95  97  12 0.01
Tue 09/01 19Z 0.18 1314  95  95  12 0.01
Tue 09/01 20Z 0.15 1413  95  97  12 0.01
Tue 09/01 21Z 0.13 1413  95  99  12 0.01
Tue 09/01 22Z 0.14 1414  97  99  12 0.01
Tue 09/01 23Z 0.14 1414  97  97  12 0.01
Wed 09/02 00Z 0.12 1515  96  91  12 0.01
Wed 09/02 01Z 0.12 1516  96  80  12 0.01
Wed 09/02 02Z 0.10 1517  96  69  12 0.01
Wed 09/02 03Z 0.11 1517  96  47  12 0.01
Wed 09/02 04Z 0.08 1619  97  54  12 0.01
Wed 09/02 05Z 0.05 1620  97  54  13 0.02
Wed 09/02 06Z 0.05 1620  97  39  13 0.02
Wed 09/02 07Z 0.04 1619  97  38  13 0.02
Wed 09/02 08Z 0.05 1719  97  45  13 0.01
Wed 09/02 09Z 0.04 1719  97  31  13 0.02
Wed 09/02 10Z 0.05 1719  97  18  13 0.02
Wed 09/02 11Z 0.10 1818  98  33  12 0.01

Run total areal avg QPF for the Central_Greens is: 0.36 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